Question

Which circles have an area of 16pi in2?



Choose all answers that are correct.









A.

a circle with a radius of 2 in.








B.

a circle with a radius of 4 in.








C.

a circle with a diameter of 8 in.








D.

a circle with a diameter of 16 in.

Answer 1

do you know formula for area of a circle ?

Answer 2

To find the area of a circle you have to solve

\(\bf \large \pi r^2\)

Answer 3

Now \(\bf r \) is the radius.

Answer 4

@jhonyy9 yes its area= pixradious squared

Answer 5

In the answer choices they have given you the radius. So plug in each radius into the formula and find which one has the answer of 16 pi in squared

Answer 6

@AihberKhan can u help me through it?

Answer 7

Sure! :)

@parisjackson

Answer 8

got my paper, lets go

Answer 9

Haha Okay xD

So the 1st one, when you plug in 2 for r it should look like \(2 \pi in^2\)

Answer 10

And that is NOT what we want. So we can eliminate A.

Answer 11

got it

Answer 12

Good! :) Now the next one... for radius we have to plug in \(4\).

Why don't you do this... when you plug in 4 for \(r\) what would you get?

@parisjackson

Answer 13

4piinsquared

Answer 14

Right! :)

Now that is NOT what we want... so we can eliminate B...

Do you see the pattern? All we need is the number 16.. which answer has that number?

So what do you think the answer is? Do you know now? :)

@parisjackson

Answer 15

its d

Answer 16

Thats what I thought... but now I am looking at it and it says 16 Diameter... not radius...

None of them have 16 for radius, so there is no answer... :P

How about we ask someone else to \(\bf \text {double check}\) :)

Answer 17

@UsukiDoll

Can you double check... we are a bit confused... :)

Answer 18

@jim_thompson5910 @jhonyy9

Can you double check... we are a bit confused... :)

Answer 19

@TheSmartOne @pooja195

Can you double check... we are a bit confused... :)

Answer 20

when you plug in the radius of 2, it should be 4pi square inches

notice how 2 is squared to get 4

Answer 21

x2

Answer 22

Right but don't we need an answer that is squared?

Answer 23

A = pi*r^2

A = pi*2^2

A = pi*4

A = 4pi

Answer 24

yeah, it has to be squared

Answer 25

`Right but don't we need an answer that is squared? `

you mean the units are squared?

Answer 26

Oh wait I get it now! Yeah follow what @jim_thompson5910 is saying :)

Sorry I couldn't help you better.. :)

@parisjackson

Answer 27

think of it like this

(2 inches) * (2 inches) = (2*2)*(inches*inches) = 4*(inches)^2

only the "inches" are squared at the end

Answer 28

so a circle with radius 2 inches leads to an area of 4pi square inches

we want 16pi square inches

so r = 2 is NOT the answer

Answer 29

there's only one value of r that works

try r = 4 now

Answer 30

8???

Answer 31

4 squared = 4*4 = 16

Answer 32

`4 squared` is not the same as `4 times 2`

Answer 33

yeah yeah yeah i get it

Answer 34

you'll also use the idea that

diameter = 2*(radius)

Answer 35

for example, if the radius was 5 then the diameter is 10

diameter = 2*(radius)
diameter = 2*(5)
diameter = 10

Answer 36

omg thanks

Answer 37

np

Answer 38

so its b?

Answer 39

@jim_thompson5910

Answer 40

B) because r = 4 inches leads to an area of 16pi square inches

AND

C) because a diameter of 8 inches leads to a radius of r = 4 inches (use the formula connecting diameter and radius)

Answer 41

`a circle with a radius of 4 in.` and `a circle with a diameter of 8 in.` are the same circle (with the same area)

Answer 42

@jim_thompson5910 i have another problem almost the same. can i get some help?

Answer 43

sure

Answer 44

ok give me a second

Answer 45

What is the exact area of a circle with a diameter of ft?









A.

square feet








B.

square feet








C.

square feet








D.

square feet

Answer 46

didnt come out right