I saw this question in JEE Advanced. But in that we had to simplify it to ∫log(1+√2)02(eu+e−u)16du
But I pose the following question as to evaluate this integral in closed form.
My Attempt:
∫π2π4(2csc(x))17dx
=∫π2π4(2.2i)17(eix−e−ix)17dx
(Bit of a cheeky attempt! I know. :D)
417i∫π2π4e17ixe2ix−1dx
If we put u=eix;du=i.eixdx, then −417∫i1+i√2u16u2−1du
(Huh??!!)
417∫1+i√2iu16u2−1du
And ∫u16u2−1=u1515+u1313+u1111+u99+u77+u55+u33+u+12log(1−u)−12log(u+1)+C
But at this point I am stuck. Please can someone help?
Answer
By applying the Weierstrass substitution x=2arctant we have:
I=∫π/2π/4(2sinx)17dx=∫π/2π/4(1sinx2cosx2)17=2∫1√2−1(1+t2t)17dt1+t2
then by setting t=e−u and applying the binomial theorem it follows that:
I=2∫log(1+√2)0(eu+e−u)16du=16037316√27+25740log(1+√2).
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