Question

Solve x2 + 9x + 9 = 0.

Answer 1

X = (-b (+-)sqrt (b^2 - 4ac) / 2a

x^2 + 9x + 9 = 0
a = 1
b = 9
c = 9

x = -9 (+-) sqrt (9^2 - 4(1)(9)) / 2(1)
x = -9 (+-) sqrt (81 - 36) / 2
x = -9 (+-) sqrt (45) / 2
x = -9 (+-) sqrt (9 * 5) / 2
x = -9 (+-) (3 sqrt 5) / 2 <===

Answer 2

$x^2 + 9x + 9 = 0\\ \\ D=b^2-4ac=9^2-4*1*9=81-36= 45 \\ \\ x_{1,2}= \frac{-bб \sqrt{D} }{2a} \\ \\ x_{1,2}= \frac{-9б \sqrt{45} }{2}= \frac{-9б3 \sqrt{5} }{2}$