The integral is given as,
I= ∫ dx x( x 4 −1 )
Multiply numerator and denominator by x 3 .
I= ∫ x 3 dx x 3 ×x( x 4 −1 ) I= ∫ x 3 dx x 4 ( x 4 −1 )
Assume x 4 =t
Differentiate the above with respect to t.
4 x 3 dx=dt x 3 dx= dt 4
Substitute the values in the integral.
I= 1 4 ∫ dt t( t−1 )
Use rule of partial fraction to simplify it.
1 t( t−1 ) = A t + B ( t−1 ) 1=A( t−1 )+Bt
Substitute t=0then,
A=−1
Substitute t=1then,
B=1
Substitute the values and integrate,
I= 1 4 ∫ −dt t + 1 4 ∫ dt ( t−1 ) I= 1 4 [ −log| t |+log| t−1 | ]+C
By substituting x 4 for t, we get
I= 1 4 [ −log| x 4 |+log| x 4 −1 | ]+C I= 1 4 log| x 4 −1 x 4 |+C