Saturday, 25 August 2018

integration - Help me Evaluate this Integral




I have this problem 5x+11(x+1)(x2+1)dx




And i'm not sure how to deal with this. I've tried substitution and getting nowhere. I've peeked at the answer and there a trigonometric part with arctan. Do i use Partial fraction expansion here?



Thanks


Answer



use the partial fraction to get
5x+11(x+1)(x2+1)=38xx2+1+8x+1=3x2+18xx2+1+8x+1



details:




5x+11(x+1)(x2+1)=Ax+Bx2+1+C1+x=(Ax+B)(1+x)+C(x2+1)(x2+1)(1+x)
5x+11(x+1)(x2+1)=Ax+Ax2+B+Bx+Cx2+C(x2+1)(1+x)
A+B=5



A+C=0
B+C=11



solve these simultaneous equations to get
A=8
B=3

C=8
so the integral will be
(3x2+18xx2+1+8x+1)dx=3tan1x4log(x2+1)+8log(x+1)+C


No comments:

Post a Comment

real analysis - How to find limhrightarrow0fracsin(ha)h

How to find lim without lhopital rule? I know when I use lhopital I easy get $$ \lim_{h\rightarrow 0}...