Monday, September 14, 2015

calculus - Simpler way to compute a definite integral without resorting to partial fractions?



I found the method of partial fractions very laborious to solve this definite integral :
03x1+x2dx



Is there a simpler way to do this ?


Answer




Perhaps this is simpler.



Make the substitution x2/3=t. Giving us



2x1/33x2/3dx=dt, i.e x1/3dx=32tdt



This gives us that the integral is



I=320t1+t3 dt




Now make the substitution t=1z to get



I=32011+t3 dt



Add them up, cancel the 1+t, write the denominator (t2t+1) as (t+a)2+b2 and get the answer.


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