Question

Help me out??? first pic is the graph second is the answer choices

Answer 1

D.

Step-by-step explanation:

According to the graph, the circle has a center of (0, 0) and a radius of 4. That means that the equation of the circle will be (x - 0)^2 + (y + 0)^2 = 4^2.

x^2 + y^2 = 16

A. If you divided all terms by 20, the radius would become 16 / 20 = 8 / 10 = 0.8. That is not 1, so choice A is incorrect.

B. If you multiplied all terms by 6, the radius would be 16 * 6 = 96, which is not 144. Choice B is incorrect.

C. This choice is obviously incorrect, since it should be + y instead of - y.

D. This choice is correct. All terms are multiplied by 2.

Hope this helps!

Answer 2

Answer: Choice D. 2x^2+2y^2 = 32

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Step-by-step explanation:

The highest point of this circle is (0,4). The lowest point is (0,-4). The midpoint between the two mentioned points is (0,0). This is the center of the circle. You'll find that (0,0) is also the midpoint of the left-most and right-most points on this circle.

(h,k) = (0,0) is the center

r = 4 is the radius as it is the distance from the center to the edge of the circle

(x-h)^2 + (y-k)^2 = r^2

(x-0)^2 + (y-0)^2 = 4^2

x^2+y^2 = 16 is one way to express the equation of the circle

For some reason, your teacher has decided to multiply both sides by 2. I'm not exactly sure why. But doing so leads to...

x^2+y^2 = 16

2(x^2+y^2) = 2*16

2x^2+2y^2 = 32

This matches up with choice D.