Question

If x² + kx – 12 = 0 and k + 1 = 0, find the value of x.

Answer 1

Given:

x² + kx – 12 = 0

k + 1 = 0

⇒ k = −1

Substitute k = −1 into the equation:

x² − x − 12 = 0

Two numbers whose:

Product = −12

Sum = −1

Numbers are: −4 and 3

x² − x − 12

= x² − 4x + 3x − 12

= (x − 4) (x + 3)

= 0

x − 4 = 0

⇒ x = 4

x + 3 = 0

⇒ x = −3

x = 4 or x = −3​