NIMCET 2014 — Mathematics PYQ
NIMCET | Mathematics | 2014The value of ∫04πlog(1+tanx)dx is equal to:
Choose the correct answer:
- A.
4πlog2
- B.
6πlog2
8πlog2
Explanation
Solution
Concept:
-
Definite Integral Property: If ∫f(x)dx=g(x)+C, then ∫abf(x)dx=[g(x)]ab=g(b)−g(a).
-
Another useful property is: ∫abf(x)dx=∫abf(a+b−x)dx.
-
Trigonometric Identity: tan(4π−x)=1+tanx1−tanx.
Calculation:
Let I=∫04πlog(1+tanx)dx
Using the property ∫abf(x)dx=∫abf(a+b−x)dx, we get:
⇒I=∫04πlog[1+tan(4π−x)]dx
⇒I=∫04πlog(1+1+tanx1−tanx)dx
⇒I=∫04πlog(1+tanx2)dx
⇒I=∫04π(log2)dx−∫04πlog(1+tanx)dx
⇒I=(log2)∫04π1dx−I
⇒2I=(log2)[x]04π
⇒2I=(log2)(4π)
⇒I=8πlog2
Correct Option: 3. (8πlog2)
Explanation
Solution
Concept:
-
Definite Integral Property: If ∫f(x)dx=g(x)+C, then ∫abf(x)dx=[g(x)]ab=g(b)−g(a).
-
Another useful property is: ∫abf(x)dx=∫abf(a+b−x)dx.
-
Trigonometric Identity: tan(4π−x)=1+tanx1−tanx.
Calculation:
Let I=∫04πlog(1+tanx)dx
Using the property ∫abf(x)dx=∫abf(a+b−x)dx, we get:
⇒I=∫04πlog[1+tan(4π−x)]dx
⇒I=∫04πlog(1+1+tanx1−tanx)dx
⇒I=∫04πlog(1+tanx2)dx
⇒I=∫04π(log2)dx−∫04πlog(1+tanx)dx
⇒I=(log2)∫04π1dx−I
⇒2I=(log2)[x]04π
⇒2I=(log2)(4π)
⇒I=8πlog2
Correct Option: 3. (8πlog2)

