Q6 / 116 · NTA Abhyas (JEE Main) 2020 · Mathematics · Definite Integration

lf f x  = sin lim t→0 2x π cot −1 x t 2 , then ∫-π2π2fx dx is equal to  (where, x≠0)

  • A
    -2
  • Correct answer
    B
    -1
  • C
    0
  • D
    2

Solution

Let y=limt→0⁡2xπcot-1⁡xt2

Case-I : when x>0 then y=2xπlimt→0⁡cot-1⁡xt2=2xπ×0=0

Case-II : when x<0 then y=2xπ limt→0⁡cot-1⁡xt2=2xπ×π=2x

f(x)=sin0x>0sin2xx<0
Now, ∫ −π 2 π 2 f( x )dx= ∫ − π 2 0 sin2x dx+ ∫ 0 π 2 0   dx=− ( cos2x 2 ) − π 2 0 =− 1 2 ( 1−( −1 ) )=−1

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

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