is a way to express the definition of a circle on the coordinate plane.
Step-by-step explanation:
We know that the general equation for a circle is ( x - h )^2 + ( y - k )^2 = r^2, where ( h, k ) is the center and r is the radius. So add 21 to both sides to get the constant term to the righthand side of the equation. Then complete the square for the y terms.
