How do you integrate int (x^3-x^2+1) / (x^4-x^3)x3x2+1x4x3 using partial fractions?

1 Answer
Feb 4, 2018

The answer is =1/(2x^2)+1/x+ln(|x-1|)+C=12x2+1x+ln(|x1|)+C

Explanation:

Perform the decomposition into partial fractions

(x^3-x^2+1)/(x^4-x^3)=(x^3-x^2+1)/(x^3(x-1))x3x2+1x4x3=x3x2+1x3(x1)

=A/(x^3)+B/(x^2)+C/(x)+D/(x-1)=Ax3+Bx2+Cx+Dx1

=(A(x-1)+B(x(x-1))+C(x^2(x-1))+D(x^3))/((x^4-x^3))=A(x1)+B(x(x1))+C(x2(x1))+D(x3)(x4x3)

The denominators are the same, compare the numerators

(x^3-x^2+1)=A(x-1)+B(x(x-1))+C(x^2(x-1))+D(x^3)(x3x2+1)=A(x1)+B(x(x1))+C(x2(x1))+D(x3)

Let x=0x=0, =>, 1=-A1=A, =>, A=-1A=1

Coefficients of xx

0=A-B0=AB, =>, B=A=-1B=A=1

Coefficients of x^2x2

-1=B-C1=BC, =>, C=B+1=-1+1=0C=B+1=1+1=0

Coefficients of x^3x3

1=C+D1=C+D, D=1-C=1-0=1D=1C=10=1

Therefore,

(x^3-x^2+1)/(x^4-x^3)=-1/(x^3)-1/(x^2)+0/(x)+1/(x-1)x3x2+1x4x3=1x31x2+0x+1x1

So,

int((x^3-x^2+1)dx)x^4-x^3)=-int(1dx)/(x^3)-int(1dx)/(x^2)+int(1dx)/(x-1)((x3x2+1)dx)x4x3)=1dxx31dxx2+1dxx1

=1/(2x^2)+1/x+ln(|x-1|)+C=12x2+1x+ln(|x1|)+C