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Evaluate: ∫0πecosxecosx+e-cosxdx - Mathematics

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प्रश्न

Evaluate: `int_0^pi e^cosx/(e^cos x + e^-cos x) dx`

मूल्यांकन

उत्तर

Let I = `int_0^pi e^cos x/(e^cos x + e^-cos x) dx`    ...(i)

∴ I = `int_0^pi e^cos(pi-x)/(e^cos(pi-x) + e^-cos(pi - x)) dx      ...["Using" int_0^a f(x) dx = int_0^a f(a - x)dx]` 

or, I = `int_0^pi e^-cos x/(e^-cos x + e^ cos x)` dx    ...(ii)

On adding eqs. (i) & (ii), we get 

2I = `int_0^pi (e^cos x + e^-cos x)/(e^cos x + e^-cos x) dx`

= `int_0^pi dx`

= `[x]_0^pi = pi`

∴ I = `(pi)/2`

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2023-2024 (February) Delhi Set - 1
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