Question

Write the equation of the circle with center (3, 2) and (−6, −4) a point on the circle.

Answer 1

The equation for a circle is as followed:

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

where the center of the circle is at (h,k) and the radius of the circle is r.

We are given (h,k) and need to find the radius. To do so, we can use the distance formula to find the distance from the  center to the point on the circle:

$d= \sqrt{(x_1-x_2)^2+(y_1-y_2)^2}$

Plug in the two points:

$d= \sqrt{(3-(-6))^2+(2-(-4))^2}$

$d= \sqrt{(9)^2+(6)^2}$

$d= \sqrt{117}$

If the distance from the center to the edge of the circle is the square root of 117, then r^2 = 117.

The answer is:

$(x-3)^2+(y-2)^2=117$