Answer:
x = -3, 6
Step-by-step explanation:
First, add 18 to both sides
x² - 3x - 18 = 0
+ 18 + 18
x² - 3x = 18
Add 9/4 to both sides because that is the square of half of -3
x² - 3x + 9/4 = 18 + 9/4
Multiply both sides by 4 to get rid of the fractions
(x² - 3x + 9/4 = 18 + 9/4)4
4x² - 12x + 9 = 72 + 9 = 81
Factor the left side of the equation
(2x - 3)² = 81
√(2x - 3)² = √81
Because of the square root, this will result in a positive number and a negative number
2x - 3 = 9
2x - 3 = -9
For both equations, add 3 to both sides then divide by 2
2x - 3 = 9
+ 3 +3
2x = 12
2x/2 = 12/2
x = 6
2x - 3 = -9
+ 3 + 3
2x = -6
x = -3
