Question

Evaluate the integral x^3 (x 4 −8)^44 dx by making the substitution u = x^4 - 8

Answer 1

(x^4-8)^45 /180 +c

Explanation:

If u=x^4-8, then du=(4x^3-0)dx or du=4x^3 dx by power and constant rule.

If du=4x^3 dx, then du/4=x^3 dx. I just divided both sides by 4.

Now we are ready to make substitutions into our integral.

Int(x^3 (x^4-8)^44 dx)

Int(((x^4-8)^44 x^3 dx)

Int(u^44 du/4)

1/4 Int(u^44 dul

1/4 × (u^45 / 45 )+c

Put back in terms of x:

1/4 × (x^4-8)^45/45 +c

We could multiply those fractions

(x^4-8)^45 /180 +c