The following integral ∫ π 4 π 2 2   c o s e c   x 17   d x is equal to

The following integral π4π22 cosec x17 dx is equal to
  1. 0log1+22eu+e-u16 du
  2. 0log(1+ 2)eu+e-u17 du
  3. 0log(1+2)eu-e-u17 du
  4. 0log(1+2)2 eu-e-u16 du

Solution

π4π22cosecx17 dx
Let eu+e-u=2cosecx, x=π4u=log 1+2, x=π2u=0
 cosecx+cotx=eu  and cosec x-cotx=e-u    cotx=eu-e-u2
eu-e-udu=-2 cosecxcotxdx
π4π22cosecx17dx=-2 log 1+20eu+e-u16 du
=0log 1+22eu+e-u16 du

Asked in: JEE Advanced 2014 (Paper 2)

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