Question

An equation of circle is (x+15)^2 + (y - 21)^2 =81It asks for the coordinates of the center and the radius

Answer 1

Given the equation of a circle:

$(x+15)^2+(y-21)^2=81$

You need to remember thatthe equation of a circle has this form:

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

Where "h" is the x-coordinate of the center of the circle, "k" is the y-coordinate of the center , and "r" is the radius.

In this case, you can identify that:

$\begin{gathered} h=-15 \\ k=21 \end{gathered}$

Notice that:

$r^2=81$

Solving for "r", you get:

$\begin{gathered} r=\sqrt{81} \\ r=9 \end{gathered}$

Hence, the answer is:

- The coordinates of the center of the circle are:

$(-15,21)$

- The radius of the circle is:

$9$