Answer:
x = -9±√145 (= 3.04 or -21.04)
Explanation:
x²+18x-64 = 0 (move the constant to the right side, add 64 to both sides)
x²+18x = 64 (divide the x-term by 2, square it, then add it to both sides)
x²+18x + (18/2)²= 64 + (18/2)² (simplify)
x²+18x + 9²= 64 + 9²
x²+18x + 9²= 64 + 81
x²+18x + 9²= 145 (simplify left side using the property (a+b)² = a²+ 2ab+b²)
(x+9)² = 145 (take square root of both sides)
x+9 = ±√145
x = -9±√145 (= 3.04 or -21.04)