Question

Evaluate
$integral subscript 0 superscript straight pi over 2 end superscript fraction numerator dx over denominator 2 space cosx space plus space 4 space sinx end fraction$

Solution

Let I = $integral subscript 0 superscript straight pi over 2 end superscript space fraction numerator dx over denominator 2 space cosx space plus space 4 sinx end fraction$
Put $tan space straight x over 2 space equals space straight t comma space space space therefore space space straight x over 2 space equals space tan to the power of negative 1 end exponent straight t space space space rightwards double arrow space space space space straight x space equals space 2 space tan to the power of negative 1 end exponent straight t space space rightwards double arrow space space space dx space equals space fraction numerator 2 over denominator 1 plus straight t squared end fraction dt$
When x = 0 t = tan 0 = 0
When $straight x equals space straight pi over 2 comma space space space straight t equals space tan straight pi over 4 space equals space 1$
Also $sinx space equals space fraction numerator 2 space tan begin display style straight x over 2 end style over denominator 1 plus tan squared begin display style straight x over 2 end style end fraction space equals space fraction numerator 2 straight t over denominator 1 plus straight t squared end fraction comma space space cosx space equals space fraction numerator 1 minus tan squared begin display style straight x over 2 end style over denominator 1 plus tan squared begin display style straight x over 2 end style end fraction space equals space fraction numerator 1 minus straight t squared over denominator 1 plus straight t squared end fraction$
$therefore$ $straight I space equals space integral subscript 0 superscript 1 fraction numerator begin display style fraction numerator 2 over denominator 1 plus straight t squared end fraction end style dt over denominator 2 open parentheses begin display style fraction numerator 1 minus straight t squared over denominator 1 plus straight t squared end fraction end style close parentheses plus 4 open parentheses begin display style fraction numerator 2 straight t over denominator 1 minus straight t squared end fraction end style close parentheses end fraction space equals space integral subscript 0 superscript 1 fraction numerator dt over denominator 1 minus straight t squared plus 4 straight t end fraction$
$equals integral subscript 0 superscript 1 fraction numerator 1 over denominator 1 minus left parenthesis straight t squared minus 4 straight t right parenthesis end fraction dt space equals space integral subscript 0 superscript 1 fraction numerator dt over denominator left parenthesis 1 plus 4 right parenthesis space minus left parenthesis straight t squared minus 4 straight t plus 4 right parenthesis end fraction space equals integral subscript 0 superscript 1 fraction numerator dt over denominator left parenthesis square root of 5 right parenthesis squared minus left parenthesis straight t minus 2 right parenthesis squared end fraction$
$equals space fraction numerator 1 over denominator 2 square root of 5 end fraction open square brackets log space open vertical bar fraction numerator square root of 5 plus left parenthesis straight t minus 2 right parenthesis over denominator square root of 5 minus left parenthesis straight t minus 2 right parenthesis end fraction close vertical bar close square brackets subscript 0 superscript 1 space equals space fraction numerator 1 over denominator 2 square root of 5 end fraction open square brackets log space fraction numerator square root of 5 minus 1 over denominator square root of 5 plus 1 end fraction minus log open parentheses fraction numerator square root of 5 minus 2 over denominator square root of 5 plus 2 end fraction close parentheses close square brackets equals space fraction numerator 1 over denominator 2 square root of 5 end fraction log open parentheses fraction numerator square root of 5 minus 1 over denominator square root of 5 minus 1 end fraction cross times fraction numerator square root of 5 plus 2 over denominator square root of 5 minus 2 end fraction close parentheses equals space fraction numerator 1 over denominator 2 square root of 5 end fraction log space open parentheses fraction numerator 5 minus 2 plus square root of 5 over denominator 5 minus 2 minus square root of 5 end fraction close parentheses space equals space fraction numerator 1 over denominator 2 square root of 5 end fraction log open parentheses fraction numerator 3 plus square root of 5 over denominator 3 minus square root of 5 end fraction close parentheses equals space fraction numerator 1 over denominator 2 square root of 5 end fraction log open parentheses fraction numerator 3 plus square root of 5 over denominator 3 minus square root of 5 end fraction cross times fraction numerator 3 plus square root of 5 over denominator 3 plus square root of 5 end fraction close parentheses space equals space fraction numerator 1 over denominator 2 square root of 5 end fraction log open square brackets fraction numerator left parenthesis 3 plus square root of 5 right parenthesis squared over denominator 4 end fraction close square brackets equals space fraction numerator 1 over denominator 2 square root of 5 end fraction log open parentheses fraction numerator 3 plus square root of 5 over denominator 2 end fraction close parentheses squared space equals space fraction numerator 1 over denominator square root of 5 end fraction log open parentheses fraction numerator 3 plus square root of 5 over denominator 2 end fraction close parentheses$

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Integrals

Evaluate
$integral subscript 0 superscript straight pi over 2 end superscript fraction numerator dx over denominator 2 space cosx space plus space 4 space sinx end fraction$

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