Answer:
see explanation
Step-by-step explanation:
given x² - 6x - 21 = 0 ( add 21 to both sides )
x² - 6x = 21
to complete the square
• add ( half the coefficient of the x-term)² to both sides
x² + 2 (- 3)x +9 = 21 + 9
(x - 3)² = 30 ( take the square root of both sides )
x - 3 = ± ( add 3 to both sides )
x = 3 ±
x = 3 - = - 2.48 ( to 2 dec. places ) or
x = 3 + = 8.48 ( to 2 dec. places )