Monday, 31 August 2015

integration - Integral intfracsqrtsinxsqrtsinx+sqrtcosxdx



We have to evaluate the following integral:



sinxsinx+cosxdx




I tried this:



I multiplied both the numerator and denominator by secx
And substituted tanx=t.



But after that I got stuck.



The book where this is taken from gives the following as the answer: ln(1+t)14ln(1+t4)+122lnt22t+1t2+2t+112tan1t2+c where t=cotx


Answer



I=sinxsinx+cosxdx=tanx1+tanxdx




substitute tanx=t2 and dx=11+t4dt



I=t(1+t)(1+t4)dt=12((1+t4)+(1t4))t(1+t)(1+t4)dt



=12t1+tdt+12(tt2)(1+t2)1+t4dt



=12(1+t)11+tdt+12t+t3(t21)t411+t4dt



=t2+12ln|t+1|+142t1+t4+12t31+t4dt12t211+t4dt12t+C




all integrals are easy except J=t211+t4dt=1t2(t+t1)22dt=(tt1)(tt1)22dt


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