NIMCET 2012 — Mathematics PYQ
NIMCET | Mathematics | 2012The value of ∫0sin2xsin−1tdt+∫0cos2xcos−1tdt is:
Choose the correct answer:
- A.
4π
(Correct Answer) - B.
2π
- C.
1
- D.
None
4π
Explanation
1. Let the first integral be I1:
I1=∫0sin2xsin−1tdt
Let t=sin2θ⟹dt=2sinθcosθdθ=sin2θdθ.
When t=0,θ=0. When t=sin2x,θ=x.
I1=∫0xθ⋅sin2θdθ
2. Let the second integral be I2:
I2=∫0cos2xcos−1tdt
Let t=cos2θ⟹dt=−2cosθsinθdθ=−sin2θdθ.
When t=0,θ=π/2. When t=cos2x,θ=x.
I2=∫π/2xθ⋅(−sin2θ)dθ=∫xπ/2θsin2θdθ
3. Combine I1 and I2:
I1+I2=∫0xθsin2θdθ+∫xπ/2θsin2θdθ
Using the property ∫abf+∫bcf=∫acf:
I=∫0π/2θsin2θdθ
4. Integration by Parts:
∫uvdθ=u∫vdθ−∫(u′∫vdθ)dθ
Let u=θ,v=sin2θ:
I=[θ(2−cos2θ)]0π/2−∫0π/2(1)(2−cos2θ)dθ
I=[−2π/2cos(π)−0]+[4sin2θ]0π/2
I=[−2π/2(−1)]+[0−0]
I=4π
Correct Option:
(a) 4π
Explanation
1. Let the first integral be I1:
I1=∫0sin2xsin−1tdt
Let t=sin2θ⟹dt=2sinθcosθdθ=sin2θdθ.
When t=0,θ=0. When t=sin2x,θ=x.
I1=∫0xθ⋅sin2θdθ
2. Let the second integral be I2:
I2=∫0cos2xcos−1tdt
Let t=cos2θ⟹dt=−2cosθsinθdθ=−sin2θdθ.
When t=0,θ=π/2. When t=cos2x,θ=x.
I2=∫π/2xθ⋅(−sin2θ)dθ=∫xπ/2θsin2θdθ
3. Combine I1 and I2:
I1+I2=∫0xθsin2θdθ+∫xπ/2θsin2θdθ
Using the property ∫abf+∫bcf=∫acf:
I=∫0π/2θsin2θdθ
4. Integration by Parts:
∫uvdθ=u∫vdθ−∫(u′∫vdθ)dθ
Let u=θ,v=sin2θ:
I=[θ(2−cos2θ)]0π/2−∫0π/2(1)(2−cos2θ)dθ
I=[−2π/2cos(π)−0]+[4sin2θ]0π/2
I=[−2π/2(−1)]+[0−0]
I=4π
Correct Option:
(a) 4π

