How do you integrate (6x^2 + 1) /( (x^2)(x-1)^3)6x2+1(x2)(x1)3 using partial fractions?

1 Answer

1/x+2/(x-1)-14/(x-1)^2+3\ln|(x-1)/x|+C1x+2x114(x1)2+3lnx1x+C

Explanation:

Let

\frac{6x^2+1}{x^2(x-1)^3}=A/(x-1)+B/(x-1)^2+C/(x-1)^3+D/x+{E}/(x^2)6x2+1x2(x1)3=Ax1+B(x1)2+C(x1)3+Dx+Ex2

\frac{6x^2+1}{x^2(x-1)^3}=frac{Ax^2(x-1)^2+Bx^2(x-1)+Cx^2+(Dx+E)(x-1)^3}{x^2(x-1)^3}6x2+1x2(x1)3=Ax2(x1)2+Bx2(x1)+Cx2+(Dx+E)(x1)3x2(x1)3

6x^2+1=(A+D)x^4+(-2A+B-3D+E)x^3+(A-B+C+3D-3E)x^2+(-D+3E)x-E6x2+1=(A+D)x4+(2A+B3D+E)x3+(AB+C+3D3E)x2+(D+3E)xE

Comparing the corresponding coefficients on both the sides we get

A+D=0\ .........(1)

-2A+B-3D+E=0\ .........(2)

A-B+C+3D-3E=6\ ............(3)

-D+3E=0\ ............(4)

E=-1\ ..........(5)

Solving all above five linear equations, we get

A=3, B=-2, C=7, D=-3, E=-1

Now, setting above values , the partial fractions are given as follows

\frac{6x^2+1}{x^2(x-1)^3}=3/(x-1)-2/(x-1)^2+7/(x-1)^3-3/x-1/x^2

Now, integrating above equation w.r.t. x, we get

\int \frac{6x^2+1}{x^2(x-1)^3}\ dx=\int 3/(x-1)\ dx-\int2/(x-1)^2\ dx+\int 7/(x-1)^3\ dx-\int 3/x\ dx-\int 1/x^2\ dx

=3\int \frac{dx}{x-1}-2\int (x-1)^{-2}\ dx+7\int (x-1)^{-3}\ dx-3\int dx/x-\int x^{-2}\ dx

=3\ln|x-1|+2/(x-1)-14/(x-1)^2-3\ln|x|+1/x+C

=1/x+2/(x-1)-14/(x-1)^2+3\ln|(x-1)/x|+C