Question

X^2+y^2-4y-15=6

Rewrite the equation of a circle in standard form. State the radius r of the circle.

Answer 1

x^2 + y^2 - 4y - 15 = 6

x^2 + y^2 - 4y = 21

x^2 + y^2 - 4y + 4 = 25

x^2 + (y - 2)^2 = 5^2

r = 5