What is the radius for a circle whose equation is x2 + y2 = 64

Find the center and radius of each circle:

x2 + y2 = 36

The standard form for a circle with center at (h, k) and radius r is:

(x-h) ^2 + (y-k) ^2 = r^2

Since x^2 + y^2 = 36 is the same as:

(x-0) ^2 + (y-0) ^2 = 6^2

this cicle has center (0,0) and radius 6.