How do you integrate int (2x+1)/((x-4)(x-1)(x+7)) 2x+1(x4)(x1)(x+7) using partial fractions?

1 Answer
Dec 9, 2016

The answer is =3/11ln(∣x-4∣)-1/8ln(∣x-1∣)-13/88ln(∣x+7∣)+C=311ln(x4)18ln(x1)1388ln(x+7)+C

Explanation:

Let's do the decomposition into partial fractions

(2x+1)/((x-4)(x-1)(x+7))=A/(x-4)+B/(x-1)+C/(x+7)2x+1(x4)(x1)(x+7)=Ax4+Bx1+Cx+7

=(A(x-1)(x+7)+B(x-4)(x+7)+C(x-1)(x-4))/((x-4)(x-1)(x+7))=A(x1)(x+7)+B(x4)(x+7)+C(x1)(x4)(x4)(x1)(x+7)

Therefore,

2x+1=A(x-1)(x+7)+B(x-4)(x+7)+C(x-1)(x-4)2x+1=A(x1)(x+7)+B(x4)(x+7)+C(x1)(x4)

Let x=1x=1, =>,3=-24B3=24B, =>, B=-1/8B=18

Let x=4x=4, =>,9=33A9=33A, =>, A=3/11A=311

Let x=-7x=7, =>, -13=88C13=88C, =>C=-13/88C=1388

So,

(2x+1)/((x-4)(x-1)(x+7))=(3/11)/(x-4)-(1/8)/(x-1)-(13/88)/(x+7)2x+1(x4)(x1)(x+7)=311x418x11388x+7

int((2x+1)dx)/((x-4)(x-1)(x+7))=3/11intdx/(x-4)-1/8intdx/(x-1)-13/88intdx/(x+7)(2x+1)dx(x4)(x1)(x+7)=311dxx418dxx11388dxx+7

=3/11ln(∣x-4∣)-1/8ln(∣x-1∣)-13/88ln(∣x+7∣)+C=311ln(x4)18ln(x1)1388ln(x+7)+C