Question

Here is the equation of a circle in standard form.

(x + 10)2 + (y + 9)2 = 100

What is the radius?

A. 100
B. 50
C. 10

Answer 1

c

Explanation:

OMY

I was so thrown off my the 2's

square root of 100 = 10

Answer 2

C

Explanation:

The equation is in the standard form for a circle:

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

where (h,k) is the center, and r is the radius

If we compare the 2 equations:

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

(x + 10)2 + (y + 9)2 = 100

We can see that r^2 is equal to 100. Let's set them equal to each other.

r^2=100

Since r is being squared, take the square root of both sides. This will cancel out the exponent.

`√(r^2)=√(100)`

r=10

So, our radius is 10, or choice C