Q.

Let ∫2-tanx3+tanx dx=12(αx+loge|βsinx+γcosx|)+C, where C is the constant of integration. Then α+γβ is equal to:              [2024]

1 7  
2 3  
3 1  
4 4  

Ans.

(4)

Let I=∫2-tanx3+tanx dx=∫2cosx-sinx3cosx+sinx dx

Write Numerator=λ(Differentiation of Denominator)+μ(Denominator)

2cosx-sinx=λ(-3sinx+cosx)+μ(3cosx+sinx)

⇒λ+3μ=2                 …(i)

and -3λ+μ=-1                   …(ii)

From equations (i) and (ii), λ=μ=12

I=12∫-3sinx+cosx3cosx+sinx dx+12∫3cosx+sinx3cosx+sinx dx

=12∫dtt+12∫dx  [Putting 3cosx+sinx=t in first integral ⇒(-3sinx+cosx) dx=dt]

=12ln(t)+12x+C

=12ln|3cosx+sinx|+12x+C

=12(αx+loge|βsinx+γcosx|)+C  (∵Given)

⇒α=1, β=1, γ=3

Now, α+γβ=1+31=4