Equation of a Circle

Question

Find an equation of the circle that satisfies the given conditions.

Center (−a, a) and radius 5a

Answer 1

So this question is testing to see if you have the equation of a circle memorized. If not, it is well worth your time (as you will need it in many future math classes). Here it is: (x - h)² + (y - k)² = r²

1. (h, k) is the center of the circle
2. r is the radius of the circle
3. Center (−a, a) and radius 5a, just plug the (h,k) and r into the equation above
4. h = -a; k = a; r = 5a
5. (x - -a)² + (y - a)² = (5a)² simplify
6. (x +a)² + (y - a)² = 25a²