Answer:
x = 5
Step-by-step explanation:
The area (A) o a rectangle is calculated as
A = lb ( l is length and b the breadth ), thus
x² + x - 12 × [tex]\frac{x+9}{x-3}[/tex] = 126 ← factor the quadratic
(x + 4)(x - 3) × [tex]\frac{x+9}{x-3}[/tex] = 126 ← cancel the common factor (x - 3)
(x + 4)(x + 9) = 126 ← expand factors using FOIL
x² + 13x + 36 = 126 ( subtract 126 from both sides )
x² + 13x - 90 = 0 ← in standard form
(x + 18)(x - 5) = 0 ← in factored form
Equate each factor to zero and solve for x
x + 18 = 0 ⇒ x = - 18
x - 5 = 0 ⇒ x = 5
However x > 0 ⇒ x = 5
