NIMCET 2012 — Mathematics PYQ
NIMCET | Mathematics | 2012The value of integral ∫0π/2logtanxdx is:
Choose the correct answer:
- A.
π
- B.
2π
- C.
3π
0
Explanation
1. Let the integral be I:
I=∫0π/2log(tanx)dx…(Equation 1)
2. Using the property ∫0af(x)dx=∫0af(a−x)dx:
I=∫0π/2log(tan(π/2−x))dx
Since tan(π/2−x)=cotx:
I=∫0π/2log(cotx)dx…(Equation 2)
3. Adding Equation 1 and Equation 2:
2I=∫0π/2[log(tanx)+log(cotx)]dx
4. Using the logarithmic property logA+logB=log(AB):
2I=∫0π/2log(tanx⋅cotx)dx
Since tanx⋅cotx=1:
2I=∫0π/2log(1)dx
5. Final Calculation:
Because log(1)=0:
2I=∫0π/20dx
2I=0
I=0
Correct Option:
(d) 0
Explanation
1. Let the integral be I:
I=∫0π/2log(tanx)dx…(Equation 1)
2. Using the property ∫0af(x)dx=∫0af(a−x)dx:
I=∫0π/2log(tan(π/2−x))dx
Since tan(π/2−x)=cotx:
I=∫0π/2log(cotx)dx…(Equation 2)
3. Adding Equation 1 and Equation 2:
2I=∫0π/2[log(tanx)+log(cotx)]dx
4. Using the logarithmic property logA+logB=log(AB):
2I=∫0π/2log(tanx⋅cotx)dx
Since tanx⋅cotx=1:
2I=∫0π/2log(1)dx
5. Final Calculation:
Because log(1)=0:
2I=∫0π/20dx
2I=0
I=0
Correct Option:
(d) 0

