Find the equation of the circle with center at (0,0) and radius 5.
Correct: A
The general equation of a circle with center (h,k) and radius r is (x - h)^2 + (y - k)^2 = r^2. Substituting h = 0, k = 0, and r = 5 gives (x - 0)^2 + (y - 0)^2 = 5^2. Simplifying gives x^2 + y^2 = 25.