a = 1 b = -10 c = -20
Using the quadratic formula,
x = [--10 +-sqr root (100 -4*1*-20)] / 2*1
x = [10 +- sqr root (180)] / 2
x = 10/2 +- (sqr root (180) / 2)
x = 5 +- (3 * sqr root (20) / 2)
x = 5 +- (6 * sqr root (5) / 2)
x = 5 +- 3 * sqr root (5)
So the answer is #3
