A circle is centered at the point (-7, -1) and passes through the point (8, 7).

Question

The radius of the circle is ____ units. The point (-15,___ ) lies on this circle.

Answer 1

(x + 7)² + (y + 1)² = r².

To get we use point (8, 7): (8 + 7)² + (7 + 1)² = r², r² = 225 + 64 = 289 = 17².

So, equation of circle: (x + 7)² + (y + 1)² = 289

Answer 2

(x+7)^2 + (y+1)^2 = r^2

(8+7)^2 + (7+1)^2 = r^2

15^2 + 8^2 = r^2

225 + 64 = r^2

289 = r^2

17^2 = r^2

r = 17 = the radius of the circle

(x+8)^2 + (y+1)^2 = 289

(-15+7)^2 + (y+1)^2 = 289

464+ (y+1)^2 = 289

(y+1)^2 = 289-64 = 225 = 15^2

(y+1)^2 = 15^2

y+1 = 15

y= 14

The point (-15,14) lies on the circle