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Find: int_(-pi/4)^0 (1+tan"x")/(1-tan"x") "dx" - Mathematics

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Question

Find:
`int_(-pi/4)^0 (1+tan"x")/(1-tan"x") "dx"`

Sum

Solution

Let

` "I" = int_(-pi/4)^0 (1+tan"x")/(1-tan"x") "dx"`

` "I" = int_(-pi/4)^0 (1+sin"x"/cos"x")/(1-sin"x"/cos"x")"dx"`

` "I" = int_(-pi/4)^0 (cos"x"+sin"x")/(cos"x"-sin"x")"dx"`

Let
cos x - sin x = t
- (sin x + cos x) dx = dt

For x `=(-pi)/4,"t" = sqrt2` and x = 0, t = 1

`"I" = -int_(sqrt2)^1 "dt"/"t"`

`"I" = int_1^sqrt2 "dt"/"t"`

` = ["lnt"]_1^sqrt2`

` = "ln"sqrt2`

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2018-2019 (March) 65/4/3
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