Question

Solve by factoring the quadratic equation 2x2 + 13x
=
-21.

Answer 1

x = -
`(7)/(2)`, x = - 3

Explanation:

Given

2x² + 13x = - 21 ( add 21 to both sides )

2x² + 13x + 21 = 0 ← in standard form

Consider the factors of the product of the x² term and the constant term which sum to give the coefficient of the x- term

product = 2 × 21 = 42 and sum = + 13

The factors are + 6 and + 7

Use these factors to split the x- term

2x² + 6x + 7x + 21 = 0 ( factor the first/second and third/fourth terms )

2x(x + 3) + 7(x + 3) = 0 ← factor out (x + 3) from each term

(x + 3)(2x + 7) = 0 ← in factored form

Equate each factor to zero and solve for x

x + 3 = 0 ⇒ x = - 3

2x + 7 = 0 ⇒ 2x = - 7 ⇒ x = -
`(7)/(2)`