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By using the properties of the definite integral, evaluate the integral: ∫0π4log(1+tanx)dx

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Questions

By using the properties of the definite integral, evaluate the integral:

`int_0^(pi/4) log (1+ tan x) dx`

Evaluate:

`int_0^(pi/4) log (1+ tan x) dx`

Sum
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Solution

Let I = `int_0^(pi/4) log (1 + tan x) dx`            ....(1)

∴ I = `int_0^(pi/4) log [1 + tan (pi/4 - x)] dx`         `...[int_0^a f(x) dx = int_0^a f(a - x) dx]`

⇒ I = `int_0^(pi/4) log {1 + (tan  pi/4 - tan x)/(1 + tan  pi/4 tan x)}dx`

⇒ I = `int_0^(pi/4) log {1 + (1 - tan x)/(1 + tan x)} dx`

⇒ I = `int_0^(pi/4) log  2/((1 + tan x)) dx`

⇒ I = `int_0^(pi/4) log 2  dx - int_0^(pi/4) log (1 + tan x) dx`

⇒ I = `int_0^(pi/4) log 2  dx - I`        ...[From (1)]

⇒ 2I = `[x log 2]_0^(pi/4)`

⇒ 2I = `pi/4 log 2`

⇒ I = `pi/8 log 2`

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Chapter 7: Integrals - Exercise 7.11 [Page 347]

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NCERT Mathematics Part 1 and 2 [English] Class 12
Chapter 7 Integrals
Exercise 7.11 | Q 8 | Page 347

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