Question

Find the zeros of y= x2 - 4x - 9 by completing the square.

Ο Α. x = 24/13
Β. χ = 3! 13
Ο
Ο
C. = 43
Ο
Ο D. χ = -2 + 13

Answer 1

A

Explanation:

To find the zeros equate y to zero, 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 = ±
`√(13)` ( add 2 to both sides )

x = 2 ±
`√(13)` → A