A value of α such that ∫ α α + 1 d x ( x + α ) ( x + α + 1 ) = l o g e 9 8 is

A value of α such that αα+1dx(x+α)(x+α+1)=loge98 is
  1. -12
  2. 12
  3. -2
  4. 2

Solution

I=αα+1dx(x+α)(x+α+1)=αα+11x+α 1x+α+1 dx
Using partial fractions
=lnx+α-lnx+α+1αα+1
=lnx+αx+α+1 αα+1
=ln2α+12α+2-ln2α2α+1
=ln2α+122α+12-1=ln98
(2α+1)2=9
2α+1=±3
α=1 or -2.

Asked in: MHT CET Full Test 10

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