Question

Which shows one way to determine the factors of x3 + 4x2 + 5x + 20 by grouping?

x(x2 + 4) + 5(x2 + 4)
x2(x + 4) + 5(x + 4)
x2(x + 5) + 4(x + 5)
x(x2 + 5) + 4x(x2 + 5)

Answer 1

x^3 + 4x^2 + 5x + 20 = (x^3 + 4x^2) + (5x + 20)
= x^2(x + 4) + 5(x + 4)
= (x^2 + 5)(x + 4).

So the correct choice is: x2(x + 4) + 5(x + 4).