Answer:
x = 2 ± [tex]\sqrt{13}[/tex]
Step-by-step explanation:
To find the zeros let y = 0, that is
x² - 4x - 9 = 0 ( add 9 to both sides )
x² - 4x = 9
To complete the square
add ( half the coefficient of the x- term )² to both sides
x² + 2(- 2) x + 4 = 9 + 4
(x - 2)² = 13 ← take the square root of both sides
x - 2 = ± [tex]\sqrt{13}[/tex] ← add 2 to both sides
x = 2 ± [tex]\sqrt{13}[/tex]
