- #1

- 7

- 0

## Homework Statement

integrate (x^3)sqrt(x^2 + 8) dx

## Homework Equations

## The Attempt at a Solution

let x = 2sqrt(2)tan(t) ==> dx= 2sqrt(2)sec^2(t) dt

=int (x^3)sqrt(x^2 + 8) dx

=int (16sqrt(2)tan^3(t)) sqrt(8tan^2(t) + 8) (2sqrt(2)sec^2(t)) dt

=int (32 sqrt(2)) (tan^3(t)) sec^3(t) dt

my problem is till this point i compared it with the the prof. working

and he had this instead : int (16sqrt(2)tan^3(t))(2sqrt(2)sec(t)) dt

help~