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Evaluate: ∫0π215+4cosx dx - Mathematics and Statistics

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प्रश्न

Evaluate: `int_0^(pi/2) 1/(5 + 4cos x)  "d"x`

योग

उत्तर

Let I = `int_0^(pi/2) 1/(5 + 4cos x)  "d"x`

Put `tan (x/2)` = t

∴ x = 2tan−1t

∴ dx = `2/(1 + "t"^2)` dt and cos x = `(1 - "t"^2)/(1 + "t"^2)`

When x = 0, t = 0 and when x = `pi/2`, t = 1

∴ I = `int_0^1 1/(5 + 4((1 - "t"^2)/(1 + "t"^2))) xx 2/(1 + "t"^2)  "dt"`

= `2int_0^1 1/(5 + 5"t" + 4 - 4"t"^2)  "dt"`

= `2int_0^1 1/(9 + "t"^2)  "dt"`

= `2int_0^1 1/("t"^2 + 3^2)  "dt"`

= `2[1/3 tan^-1("t"/3)]_0^1`

= `2/3[tan^-1(1/3) - tan^-1(0)]`

= `2/3 tan^-1 (1/3)`

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Methods of Evaluation and Properties of Definite Integral
  क्या इस प्रश्न या उत्तर में कोई त्रुटि है?
अध्याय 2.4: Definite Integration - Short Answers II

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