Question

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

Answer 1

x = 2 ±
`√(13)`

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 = ±
`√(13)` ← add 2 to both sides

x = 2 ±
`√(13)`