If the value of the integral ∫ 0 5 x + [ x ] e x - [ x ] d x = α e - 1 + β , where α ,…

If the value of the integral 05x+[x]ex-[x]dx=αe-1+β, where α, βR, 5α+6β=0, and x denotes the greatest integer less than or equal to x; then the value of (α+β)2 is equal to :
  1. 25
  2. 100
  3. 36
  4. 16

Solution

05x+[x]ex-[x]dx=αe-1+β

01xexdx+12x+1ex-1dx+23x+2ex-2dx+34x+3ex-3dx+45x+4ex-4dx

Let x-1=p, x-2=q, x-3=r, x-4=w

01xexdx+01p+2epdp+01q+4eqdq+01r+6erdr+01w+8ewdw

01xexdx+01x+2exdx+01x+4exdx+01x+6exdx+01x+8exdx

=015x+20exdx=501x+4exdx

=5x+4e-x-101-01e-x-1dx

=5-5e-1+4+-e-1+1=5-6e-1+5=-30e-1+25

α=-30,β=25

(α+β)2=25

Asked in: JEE Main 2021 (26 Aug Shift 2)

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