Question

Which equation is the equation of a circle with a diameter of 20 cm and center at (-3, 6)?

A. (x-3)^2 + (y+6)^2 = 400
B. (x-3)^2 + (y+6)^2 = 100
C. (x+3)^2 + (y-6)^2 = 100
D. (x+3)^2 + (y-6)^2 = 400

Answer 1

the equation of a circle with centre (a,b) and radius r is:
(x - a)^2 + (y - b)^2 = r^2
thus,
here centre (a,b) = (-3,6), a = -3, b = 6
and radius = diameter/2 = 20/2 =10 units
therefore, the equation is
(x + 3)^2 + (y - 6)^2 = 100
which is c.