Question

The radius of the circle whose equation is (x - 3)² + (y + 1)² = 16 is

A). 4
B). 8
C). 16

Answer 1

Answer: OPTION A.

Explanation:

The equation of a circle in center-radius form is:

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

Where the center is at the point (h,k) and "r" is the radius.

Then, given the equation of the circle:

`(x - 3)^2 + (y + 1)^2 = 16`

You can idenfity that:

`r^2=16`

Therefore, in order to find the radius, you need to solve for "r".

Then, this is:

`r=√(16)\\\\r=4`

Answer 2

The equation of a circle is written as (x-h)^2 + (y-k)^2 = r^2

Where the center point of the circle is (h,k) and r is the radius.

In the given equation 16 = r^2

To find r take the square root of both sides:

r = √16

r = 4

The answer is A.