Answer:
b
Step-by-step explanation:
Given
3x² - 18x = 21 ( divide all terms by 3 )
x² - 6x = 7
To complete the square
add ( half the coefficient of the x- term )² to both sides
x² + 2(- 3)x + 9 = 7 + 9
(x - 3)² = 16 ( take the square root of both sides )
x - 3 = ± [tex]\sqrt{16}[/tex] = ± 4 ( add 3 to both sides )
x = 3 ± 4, hence
x = 3 - 4 = - 1 and x = 3 + 4 = 7
