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Evaluate: ∫sec x2-1dx - Mathematics

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Question

Evaluate:

`intsqrt(sec  x/2 - 1)dx`

Sum

Solution

I = `intsqrt(sec  x/2 - 1)dx`

= `intsqrt((1 - cos  x/2)/(cos  x/2)) dx`

= `intsqrt(((1 - cos  x/2)(1 + cos  x/2))/(cos  x/2(1 + cos  x/2)))dx`

= `int(sin  x/2)/sqrt(cos^2  x/2 + cos  x/2)dx`

Let `cos  x/2 = t`

`\implies -sin  x/2*1/2dx = dt`

`\implies sin  x/2*dx = -2dt`

∴ I = `-2int dt/(sqrt(t^2 + t)`

= `-2int dt/sqrt((t + 1/2)^2 - (1/2)^2`

= `-2log_e|(t + 1/2) + sqrt(t^2 + t)| + c`

= `-2log_e|(cos  x/2 + 1/2) + sqrt(cos^2  x/2 + cos  x/2)| + c`

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