Question

What substitution should be used to rewrite 6(x + 5)2 + 5(x + 5) – 4 = 0 as a quadratic equation? u = (x + 5) u = (x – 5) u = (x + 5)2 u = (x – 5)2

Answer 1

6(x+5)² + 5(x+5)-4 = 0

(x+5)(x+5) = x(x+5)+5(x+5) = x² + 5x + 5x + 25 = x² + 10x + 25

6(x²+10x+25) + 5(x+5) - 4 = 0
6x² + 60x + 150 + 5x + 25 - 4 = 0
6x² + 60x + 5x + 150 + 25 - 4 = 0
6x² + 65x + 171 = 0

u = (x + 5)