Question

Determine the equation of the circle graphed below. The center's numbers are 4 and -7. The radius is -7. The circle is at the left bottom side of the graph.

Answer 1

The radius must be nonnegative, so use r = |−7| = 7. With center (h,k) = (4,−7) the circle is

(x − 4)^2 + (y + 7)^2 = 7^2 = 49.

Expanded form: x^2 + y^2 − 8x + 14y + 16 = 0.