Need some help thanks

 Need Some Help Thanks

Answers

Answer 1

In the given equations, the value of variables are:

(A) a = -10(B) b = -0.2(C) c = 0.25

What exactly are equations?When two expressions are equal in a mathematical equation, the equals sign is used to show it.A mathematical statement is called an equation if it uses the word "equal to" in between two expressions with the same value.Using the example of 3x + 5, the result is 15.There are many different types of equations, such as cubic, quadratic, and linear.The three primary categories of linear equations are point-slope, standard, and slope-intercept equations.

So, solving for variables:

(A) 1/5a = -2:

1/5a = -2a = -2 × 5a = -10

(B) 8 + b = 7.8:

8 + b = 7.8b = 7.8 - 8b = -0.2

(C) -0.5 = -2c:

-0.5 = -2cc = -0.5/-2c = 0.25

Therefore, in the given equations, the value of variables are:

(A) a = -10(B) b = -0.2(C) c = 0.25

Know more about equations here:

brainly.com/question/2972832

#SPJ13


Related Questions

A ball is thrown from an initial height of 4 feet with an initial upward velocity of 23 ft/s. The ball's height h (in feet) after 1 seconds is given by the following.h=4+231-167Find all values of 1 for which the ball's height is 12 feet.Round your answer(s) to the nearest hundredth.(If there is more than one answer, use the "or" button.)Please just provide the answer my last tutor lost connection abruptly.

Answers

Answer

t = 0.59 seconds or t = 0.85 seconds

Step-by-step explanation:

[tex]\begin{gathered} Given\text{ the following equation} \\ h=4+23t-16t^2\text{ } \\ h\text{ = 12 f}eet \\ 12=4+23t-16t^2 \\ \text{Collect the like terms} \\ 12-4=23t-16t^2 \\ 8=23t-16t^2 \\ 23t-16t^2\text{ = 8} \\ -16t^2\text{ + 23t - 8 = 0} \\ \text{ Using the general formula} \\ t\text{ }=\text{ }\frac{-b\pm\sqrt[]{b^2\text{ - 4ac}}}{2a} \\ \text{let a = -16, b = 23, c = -8} \\ t\text{ = }\frac{-23\pm\sqrt[]{(23)^2\text{ - 4}\cdot\text{ }}(-16)\text{ x (-8)}}{2(-16)} \\ t\text{ = }\frac{-23\pm\sqrt[]{529\text{ - 512}}}{-32} \\ t\text{ = }\frac{-23\pm\sqrt[]{17}}{-32} \\ \text{t = -23+}\frac{\sqrt[]{17}}{-32}\text{ or -23-}\frac{\sqrt[]{17}}{-32} \\ t\text{ = -23 }+\text{ 4.12/-32 or t = }\frac{-23\text{ - 4.12}}{-32} \\ t\text{ = }0.59\text{ seconds or t =0.85 seconds} \end{gathered}[/tex]

Therefore, t = 0.59 seconds or t = 0.85 seconds

Solve each system of the equation by elimination. y=-4x+14y=10x-28

Answers

Explanation:

The elimination method consists in substracting one equation from the other, so you eliminate one of the variables and you have only one equation to solve for one variable.

In this case, y has the same coefficient in both equations, so this is the variable we will eliminate.

Substract the first equation from the second:

[tex]\begin{gathered} y=10x-28 \\ - \\ y=-4x+14 \\ \text{ ---------------------} \\ y-y=10x+4x-28-14 \\ 0=14x-42 \end{gathered}[/tex]

And solve for x:

[tex]\begin{gathered} 14x=42 \\ x=\frac{42}{14} \\ x=3 \end{gathered}[/tex]

Now, we replace x = 3 into one of the equations and solve for y:

[tex]y=-4\cdot3+14=-12+14=2[/tex]

Answer:

• x = 3

,

• y = 2

Jerome rolls two six-sided number cubes. What is the probability that he rolls doubles, given the sum of the numbers is 8?

Answers

Answer:

[tex]\frac{1}{6}[/tex]

Step-by-step explanation:

hope you get it thats the last pen that works in my house

Answer:  There are five possible outcomes with a sum of 8:

2 and 6,

3 and 5,

4 and 4,

5 and 3,

6 and 2.

There is only one outcome, 4 and 4, that is doubles. Therefore, the probability is 1/5.

Step-by-step explanation: Got it right on Edmentum

Drag the correct algebraic representation of the reflection to the white box

Answers

Question 1

When any point (x,y) is reflected over the x-axis, the reflection coordinate is (x,-y).

So, the x coordinate remains the same, and the y coordinate goes negative.

A = ( -6, 6 ) → A' = (-6,-6 )

B = (-2,6 ) → B' = (-2,-6)

C= (-6,1 ) → C' = (-6,- 1)

Algebraic representation: ( x, -y )

Lines that are perpendicular have slopes that arethe same or opposite and reciprocal.

Answers

When lines are perpendicular the slopes of both are opposite and reciprocal, that is:

[tex]m\text{ and - }\frac{1}{m}[/tex]

In words, if we have a line with slope = m, the perpendicular line to that line will have a slope = - 1/m ( opposite and reciprocal).

create an original function that has at least one asymptote and possibly a removable discontinuity list these features of your function: asymptote(s) (vertical horizontal slant) removable discontinuity(ies) x intercept(s) y intercept and end behavior provide any other details that would enable another student to graph and determine the equation for your function do not state your function

Answers

We have to create a function that has at least one asymptote and one removable discontinuity (a "hole").

We then have to list the type of feature.

We can start with a function like y = 1/x. This function will have a vertical asymptote at x = 0 and a horizontal asymptote at y = 0.

We can translate it one unit up and one unit to the right and write the equation as:

[tex]y=\frac{1}{x-1}+1=\frac{1}{x-1}+\frac{x-1}{x-1}=\frac{x}{x-1}[/tex]

Then, the asymptotes will be x = 1 and y = 1. We have at least one asymptote for this function.

We can now add a removable discontinuity. This type of discontinuity is one that is present in the original equation but, when factorizing numerator and denominator, it can be cancelled. This happens when both the numerator and denominator have a common root: the rational function can be simplified, but the root is still present in the original expression.

We than can add a removable discontinuity to the expression by multiplying both the numerator and denominator by a common factor, like (x-2). This will add a removable discontinuity at x = 2.

We can do it as:

[tex]y=\frac{x(x-2)}{(x-1)(x-2)}=\frac{x^2-2x}{x^2-3x+2}[/tex]

This will have the same shape as y =x/(x-1) but with a hole at x = 2, as the function can not take a value that makes the denominator become 0, so it is not defined for x = 2.

Finally, we can find the x and y intercepts.

The y-intercepts happens when x = 0, so we can calculate it as:

[tex]\begin{gathered} f(x)=\frac{x^2-2x}{x^2-3x+2} \\ f(0)=\frac{0^2-2\cdot0}{0^2-3\cdot0+2}=\frac{0}{2}=0 \end{gathered}[/tex]

The y-intercept is y = 0, with the function passing through the point (0,0).

As the x-intercept is the value of x when y = 0, we already know that the x-intercept is x = 0, as the function pass through (0,0).

Then, we can list the features as:

Asymptotes: Vertical asymptote at x = 1 and horizontal asymptote at y = 1.

Removable discontinuity: x = 2.

y-intercept: y = 0.

End behaviour: the function tends to y = 1 when x approaches infinity or minus infinity.

With that information, the function can be graphed.

A cashier has 24 bills, all of which are $10 or $20 bills. The total value of the money is $410. How many of each type of bill does the cashier have?

Answers

The cashier has 7 bills of $10 and 17 bills of $20 (found using linear equation).

According to the question,

We have the following information:

A cashier has 24 bills, all of which are $10 or $20 bills. The total value of the money is $410.

Now, let's take the number of $10 bills to be x and the number of $20 bills to be y.

So, we have the following expression:

x+y = 24

x = 24-y .... (1)

10x+20y = 410

Taking 10 as a common factor from the terms on the left hand side:

10(x+2y) = 410

x+2y = 410/10

x+2y = 41

Now, putting the value of x from equation 1:

24-y+2y = 41

24+y = 41

y = 41-24

y = 17

Now, putting this value of y in equation 1:

x = 24-y

x = 24-17

x = 7

Hence, the cashier has 7 bills of $10 and 17 bills of $20 when the total value of the money is $410.

To know more about linear equation here

https://brainly.com/question/13738061

#SPJ1

Find f(x) • g(x) if f(x) = x2 – 7 and g(x) = x2 + 3x + 7

Answers

Given the functions:

[tex]\begin{gathered} f(x)=x^2-7 \\ g(x)=x^2+3x+7 \end{gathered}[/tex]

We will find: f(x) • g(x)

So, we will find the product of the functions

We will use the distributive property to get the result of the multiplications

So,

[tex]\begin{gathered} f\mleft(x\mright)•g\mleft(x\mright)=(x^2-7)\cdot(x^2+3x+7) \\ f\mleft(x\mright)•g\mleft(x\mright)=x^2\cdot(x^2+3x+7)-7\cdot(x^2+3x+7) \\ f\mleft(x\mright)•g\mleft(x\mright)=x^4+3x^3+7x^2-7x^2-21x-49 \\ f\mleft(x\mright)•g\mleft(x\mright)=x^4+3x^3-21x-49 \end{gathered}[/tex]

so, the answer will be:

[tex]f\mleft(x\mright)•g\mleft(x\mright)=x^4+3x^3-21x-49[/tex]

Find 8 3/4 ÷ 1 2/7. Write the answer in simplest form.

Answers

Problem: Find 8 3/4 ÷ 1 2/7. Write the answer in the simplest form.​

Solution:

[tex](8+\frac{3}{4}\text{ )}\div(1\text{ + }\frac{2}{3})[/tex]

this is equivalent to:

[tex](\frac{32+3}{4}\text{ )}\div(\text{ }\frac{3+2}{3})\text{ = }(\frac{35}{4}\text{ )}\div(\text{ }\frac{5}{3})\text{ }[/tex]

Now, we do cross multiplication:

[tex]=(\frac{35}{4}\text{ )}\div(\text{ }\frac{5}{3})=\frac{35\text{ x 3}}{5\text{ x 4}}\text{ =}\frac{105}{20}[/tex]

then, the correct answer would be:

[tex]=\frac{105}{20}[/tex]

Find the x- and y-intercepts for the following equation. Then use the intercepts to graph the equation.
4x + 2y = 8

Answers

Answer:

Step-by-step explanation:

x int=2

y int=4

graph 2,0 and 0,4 as two points

2.) On the first night of a concert, Fish Ticket Outlet collected $67,200 on the sale of 1600 lawn
seats and 2400 reserved seats. On the second night, the outlet collected $73,200 by selling
2000 lawn seats and 2400 reserved seats. Solve the system of equations to determine the cost
of each type of seat.

Answers

Answer:

L=$15

R=$18

Step-by-step explanation:

i cant really explain the work

A rectangular field of corn is averaging 125 bu/acre. The field measures 1080 yd by 924 yd. How many bushels of corn will there be?

Answers

Based on the dimensions of the rectangular field, and the corn per acre, the number of bushels of corn can be found to be 25,772 bushels

How to find the number of bushels of corn?

First, find the area of the rectangular field:

= 1,080 x 924

= 997,920 yard²

Then convert this to acres with a single acre being 4,840 yards²:
= 997,920 / 4,840 square yards per acre

= 206.18 acres

The number of bushels of corn that can be grown is:

= 206.18 x 125 bushel per acre

= 25,772 bushels

Find out more on the number of bushels per acre at https://brainly.com/question/27316464

#SPJ1

Find the volume of a pyramid with a square base, where the side length of the base is19.3 ft and the height of the pyramid is 16.2 ft. Round your answer to the nearesttenth of a cubic foot.

Answers

Find the volume of a pyramid with a square base, where the side length of the base is

19.3 ft and the height of the pyramid is 16.2 ft. Round your answer to the nearest

tenth of a cubic foo

Remember that

the volume of the pyramid is equal to

[tex]V=\frac{1}{3}\cdot B\cdot h[/tex]

where

B is the area of the base

h is the height

step 1

Find out the area of the base

B=19.3^2

B=372.49 ft2

h=16.2 ft

substitute the given values in the formula

[tex]V=\frac{1}{3}\cdot372.49\cdot16.2[/tex]V=2,011.4 ft3

May I please get help with this I have tried multiple times to get the correct answer but still could not get them right. I am confused on how I should draw the dilation as I have tried many times as well.

Answers

After performing dilation centered at the origin we get

(a) shortest side of original figure=2 units

   shortest side of the final figure=6units

(b) shortest side of the final figure=3×shortest side of the original figure

(c) True

(d) False

What is the dilation of the figure centered at origin?

A transformation called a dilatation alters a figure's size without altering its shape. A figure might become larger or smaller due to dilation. For instance.

The image is smaller than the preimage when the scaling factor is between 0 and 1. Reductions are referred to as dilations with scale factors between 0 and 1.

The image is larger than the preimage if the scaling factor is greater than 1. Enlargements are defined as a dilation with a scale factor greater than 1.

To get the size of the edge we multiply the size of original lenght by scale factor.

To learn more about Dilation of Figure visit:

https://brainly.com/question/20810552

#SPJ13

Use the drawing tools to the graph the solution to this system of inequalities on the coordinate plane.
y> 2x + 4
x+y≤6

Answers

The solution to the system of inequalities y> 2x + 4 , x+y≤6 on the coordinate plane is shown below .

in the question ,

the system of inequality is given

y> 2x + 4

x+y≤6

to plot these inequalities on the coordinate plane ,we need to find the intercepts of both.

y>2x+4

put x = 0 we get y as 4   , (0,4)

put y = 0 we get x as -2   ,(-2,0)

x+y≤6

put x = 0  , we get y as 6    , (0,6)

put y = 0 , we get x as 6 ,    (6,0)

the solution of both the inequality is shown below .

Therefore , the solution to the system of inequalities y> 2x + 4 , x+y≤6 on the coordinate plane is shown below .

Learn more about Inequality here

https://brainly.com/question/21857626

#SPJ1

I attached the questions as images. The first image is actually the second.You can send in the work on paper like the graphing part.The questions can be typed on the solution tab or messages whichever is easier for you.Thanks again for the help :)

Answers

SOLUTION

Consider the image below,

The lenght of the compass is the radius, using a lenght of 5 unit, we have circle below as the sphere .

Where

[tex]\begin{gathered} r=\text{ radius, O= origin } \\ And \\ r=5\text{unit } \end{gathered}[/tex]

Using the formula, we have

[tex]\begin{gathered} \text{Volume of sphere} \\ =\frac{4}{3}\pi r^3 \\ \text{where} \\ \pi=3.14,\text{ r=}5 \end{gathered}[/tex]

Substitute into the formula, we have

[tex]\begin{gathered} \text{Volume of the sphere is } \\ =\frac{4}{3}\times3.14\times5^3 \\ \text{Hence } \\ 523.33\text{ cubic unit} \end{gathered}[/tex]

Therefore

The volume of the sphere is 523.33 cubic unit

I can’t see the pictures they won’t load so I’ll try to turn off my phone and turn it back on and I’ll answer the question

Solve by factoring. Be sure to look for a GCF first in case there is one-2x²-4x+70=0

Answers

ANSWER

x = 5 and x = -7

EXPLANATION

We want to solve the equation by factoring.

The equation is:

[tex]-2x^2\text{ - 4x + 70 = 0}[/tex]

First, there is a greatest common factor that we can use to simplify the equation. That is -2, so, first we divide through by -2.

It becomes:

[tex]x^2\text{ + 2x - 35 = 0}[/tex]

Now, factorise:

[tex]\begin{gathered} x^2\text{ + 2x - 35 = 0} \\ x^2\text{ + 7x - 5x - 35 = 0} \\ x(x\text{ + 7) - 5(x + 7) = 0} \\ (x\text{ - 5)(x + 7) = 0} \\ x\text{ = 5 and x = -7} \end{gathered}[/tex]

Not sure on how to do this. Would really like some help.

Answers

Given:

[tex]\cos60^{\circ}[/tex]

To find:

The value

Explanation:

We know that,

[tex]\cos\theta=\sin(90-\theta)[/tex]

So, we write,

[tex]\begin{gathered} \cos60^{\circ}=\sin(90-60) \\ =\sin30^{\circ} \\ =\frac{1}{2} \end{gathered}[/tex]

Final answer:

[tex]\cos60^{\circ}=\frac{1}{2}[/tex]

•is this function linear? •what’s the pattern in the table•what would be a equation that represents the function

Answers

Given data:

The given table.

The given function can be express as,

[tex]\begin{gathered} y-0=\frac{2-0}{1-0}(x-0) \\ y=2x \end{gathered}[/tex]

As the equation of the above function is in the form of y=2x, it is linear function because for single value of x we got single value of y.

Thus, the function can be express as y=2x form which is linear function.

What type of number is - Choose all answers that apply:AWhole numberBIntegerRationalDIrratio

Answers

It is whole, integer, rational

Determine the frequency of each class and the table shown

Answers

Given:

The dataset and table with class.

Required:

Determine the frequency of each class.

Explanation:

Answer:

Answered the question.

Which of the following statements are true regarding functions? Check all that apply. A. The horizontal line test may be used to determine whether a function is one-to-one. B. The vertical line test may be used to determine whether a relatio is a function. C. A sequence is a function whose domain is the set of rational numbers. PREVIOUS

Answers

Statement A is true.

In the next example, we can see a function that is not one-to-one with the help of the horizontal line test:

Statement B is true.

In the next example, we can see a relationship that is not a function because it doesn't pass the vertical line test

Statement C is false.

A sequence is a function whose domain is the set of natural numbers

what is the image of -3 -7 after a reflection over the x-axis

Answers

Given the point (-3, -7)

We need to find the image after a reflection over the x-axis

The rule of reflection over the x-axis is:

[tex](x,y)\rightarrow(x,-y)[/tex]

So, the image of the given point will be:

[tex](-3,-7)\rightarrow(-3,7)[/tex]

so, the answer is option D. (-3, 7)

When we use function notation, f(x)=# is asking you to find the input when the output is the given number. We can also consider that an ordered pair can be written as (x,#). With this is mind, explain why f(x)=0 is special.

Answers

Notice that f(x)=0 is special because is the intercept of the graph with the x-axis and if f(x) corresponds to a function, the x-intercepts are the roots of the function.

The ordered pair can be written as (x,0), where x is such that f(x)=0.

5 ptsIn Ms. Johnson's class a student will get 3 points forhaving their name on their paper and 4 points for eachquestion that is correct. In Mr. Gallegos class, a studentwill get 7 points for having their name on their paper and2 points for each question correct. Which inequalitycould be used to determine x, the number of questionsthat would give you a higher grade in Ms. Johnson'sclass?

Answers

In Ms. Johnson's class a student will get 3 points for

having their name on their paper and 4 points for each

question that is correct. In Mr. Gallegos class, a student

will get 7 points for having their name on their paper and

2 points for each question correct. Which inequality

could be used to determine x, the number of questions

that would give you a higher grade in Ms. Johnson's

class?

we have

Ms. Johnson's class

3+4x

Mr. Gallegos class

7+2x

so

the inequality is given by

3+4x > 7+2x

solve for x

4x-2x > 7-3

2x>4

x> 2

the number of question must be greater than 2

Evaluate the expression when a=3 and b=6. b2-4a

Answers

b² - 4a

evaluated when a = 3 and b = 6 is:

6² - 4(3) =

= 36 - 12=

= 24

How do I find x I know you separate the shapes but I got it wrong…

Answers

Let's find this length first

6√2 is the hypotenuse, then

[tex]\begin{gathered} (6\sqrt{2})^2=6^2+y^2 \\ \\ y^2=(6\sqrt{2})^2-6^2 \\ \\ y^2=36\cdot2-36 \\ \\ y^2=36 \\ \\ y=\sqrt{36}=6 \end{gathered}[/tex]

Then we can find x because

[tex]\begin{gathered} x^2=y^2+12^2 \\ \\ x^2=6^2+12^2 \\ \\ x^2=36+144 \\ \\ x^2=180 \\ \\ x=\sqrt{180} \\ \\ x=6\sqrt{5} \end{gathered}[/tex]

The length of x is

[tex]x=6\sqrt{5}[/tex]

Write an equation of the line passing through the point (8,-3) that is parallel to the line y= -x -1. An equation of the line is

Answers

The equation of the line, in slope-intercept form, that is parallel to the line y = -x - 1 is: y = -x + 5.

How to Write the Equation of Parallel Lines?

Parallel lines have equal slope value, "m". In slope-intercept form, the equation y = mx + b represents a line, where the slope is "m" and the y-intercept is "b".

The slope of y= -x -1 is -1. This means the line that is parallel to y= -x -1 will also have a slope that is equal to -1.

Substitute m = -1 and (x, y) = (8, -3) into y = mx + b to find the value of b:

-3 = -1(8) + b

-3 = -8 + b

-3 + 8 = b

5 = b

b = 5

Substitute b = 5 and m = -1 into y = mx + b to wrote the equation of the line that is parallel y = -x -1:

y = -x + 5

Learn more about the equation of parallel lines on:

https://brainly.com/question/11345748

#SPJ1

Given a function described by the table below, what is y when x is 5?XY264859612

Answers

Given a function described by the table

We will find the value of (y) when x = 5

As shown in the table

When x = 5, y = 9

so, the answer will be y = 9

The top-selling Red and Voss tire is rated 60000 miles, which means nothing. In fact, the distance the tires can run until wear-out is a normally distributed random variable with a mean of 72000 miles and a standard deviation of 7000 miles.A. What is the probability that the tire wears out before 60000 miles?Probability = What is the probability that a tire lasts more than 80000 miles? Probability=

Answers

a. 0.0436

b. 0.1271

We are given the following:

Distance (x) = 60,000

Mean (u) = 72,000

Standard Deviation(s) = 7,000

We are also told that it is a normal disribution relationship. The formula for ND is as follows:

z = (x - u) / s

Now we can continue with part a and b as follows:

a) P (x < 60,000)

= P (z < (60000 - 72000) / 7000)

= P (z < -1.714)

We can find the corresponding z score by looking at a z score table, and we find th probability to be 0.0436

b) P ( x > 80,000)

= P(z > (80000 - 72000) / 7000)

= P( z > 1.143)

We find the corresponding z score to be 0.8729, now we can substract this from 1 sinsce our probability is larger than the given distance (meaning we are trying to find the area to the right of the z score) to find our final answer:

1 - 0.8729 = 0.1271

Other Questions
Whats the correct answer answer asap for brainlist please gravity always tries to collapse the mass of a star toward its center. what mechanism can oppose this gravitational collapse for a star? question 5 options: solar wind pressure convective movement of gases magnetic field pressure radiation pressure in 2001, a worm exploited vulnerabilities in microsoft internet information services (iis) to infect over 250,000 systems in under nine hours. what was this worm called? What is the value of the expression 2c( a + b) when a = 2, b = 5, and c = 4 Find the equation of the linear function represented by the table below in slope-intercept form.xy1-82-123-164-20 The coordinates of quadrilateral ABCD are A (-6,2) B (-5,3) C (7,3) D (0,4). What are the coordinates of the image if the quadrilateral is translated 4 units down and 3 units right Gwen says that the sum of -1 3/4 and 2 1/2 is the same as the difference between 2 1/2 and 1 3/4 is Gwen correct explain why or why not List the elements in the set{x 1 x is a negative multiple of 5} i am stuck on this question. any help would be greatly appreciated william i. thomas notes that people respond not only to the objective features of a person or situation but also to the meaning that the person or situation has for them. this view represents which sociological perspective? There is a total of $4,840 in an account after 2 years of earning compound interest at a rate of 10%. What was the original amount invested? Select the correct answer from each drop-down menu.When historians want to evaluate a primary source in the form of human remains, they send the remains to . These professionals study the remains and share their knowledge with historians. When historians want to locate a written source about an ancient human culture, they may ask . These professionals help historians find books on the subject written by reliable authors. what is the hazard posed by small (150 m) twisting vortices being pulled into the eyewall of a hurricane? multiple choice question. the side of vortices spinning in the same direction as the eyewall will blow even faster, as the eyewall wind speed is added to its own. they can become trapped within the otherwise calm eye and form into tornadoes. the vortice can separate the eye from the hurricane and cause a tornado to form in its place. they are pushed downward by the eyewall, causing strong downbursts. Find x rounded to the nearest whole degree. Be sure to round correctly! Given the venn diagram below, what is the correct notation?A. B. (MF)C. (MF)D. none of these Help This is due at the end of class what fluid property is responsible for the development of the velocity boundary layer? for what kinds of fluids will there be no velocity boundary layer in a pipe? 20) g(a) = a - 2h(a) = -3aFind g(a) + h(a) Why where ignatius of loyola and teresa of avila so important to the counter reformation HELP The volume of cylinder is 504 pi cm^(3) & height is 14cm Find the curved surface area 8 total surface area.