Question

If the radius of a circle is doubled, what happens to the area?

Answer 1

@bibby

Answer 2

let's draw a circle with radius 2.
what's the area? (keep it in terms of pi_

Answer 3

3.14 x 4

Answer 4

\(C_2=2^2\pi=4\pi\\C_4=4^2\pi=16\pi\\\) (the subscript stands for the radius)

Answer 5

what happened to the area?`

Answer 6

I'm confused..

Answer 7

a=12.56 ?

Answer 8

C_2 is a circle with radius 2. it's area is 4pi
C_4 is a circle with radius 2. it's area is 16pi

do you see a relationship?

Answer 9

I said to keep it in terms of pi so we don't have to deal with decimals

Answer 10

Yes, I do.

Answer 11

it might be easier to just replace r with 2r
circle one area = \(\pi r^2\)
circle two area = \(\pi (2r)^2=\pi 4r^2=4 \pi r^2\)

Answer 12

But to find the area, I did what you just said for circle one.

Answer 13

keeping something in terms of pi means not multiplying by 3.14.

Answer 14

Okay..

Answer 15

I don't understand what you don't understand. Use your words

Answer 16

Okay. I don't understand anything after you drew out the circle.

Answer 17

okay. basically, I'm using the area formula for a circle
once on a circle with radius "r"

then again, on a circle with radius "2r" (double the radius, as per the question)

Answer 18

Right.