Question

Find a:

(x+3)(x+a)(x+7)=x³+15x²+71x+105

Answer 1

a = 5

Explanation:

(x+3)(x+a)(x+7)=x³+15x²+71x+105

(x+3)(x+a)(x+7) = (x²+10x+21)(x+a) = x³ + (10+a)x² + (21+10a)x + 21a

21a = 105

a = 5

check: 21 + 10a = 71 ... 71x

10 + q = 15 .... 15x²