Q41 / 75 · JEE Main 2020 (09 Jan Shift 2) · Mathematics

If ∫dθcos2θtan2θ+sec2θ= λtanθ+2logefθ+C where C is a constant of integration, then the ordered pair λ,fθ is equal to:

  • A
    1,1-tanθ
  • B
    -1,1-tanθ
  • Correct answer
    C
    -1,1+tanθ
  • D
    1,1+tanθ

Solution

∫sec2θ1+tan2θ1-tan2θ+2tanθ1-tan2θdθ

=∫sec2θ1-tan2θ1+tanθ2dθ

=∫sec2θ1-tanθ1+tanθdθ

Let tanθ=t⇒sec2θdθ=dt

=∫1-t1+tdt=∫-1+21+tdt

=-t+2ln1+t+C

=-tanθ+2ln1+tanθ+C

⇒λ=-1 and fθ=1+tanθ

Hence, the correct answer is option: 'C'.

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