2 1 ∫ − π / 2 π / 2 1 − ( 2 − 1 ) 2 sin 2 θ d θ = A C / D π A + B Γ ( E B ) Γ ( E F )
The equation above holds true positive integers A , B , C , D , E and F such that A is square-free and C , D are coprime. Find A + B + C + D + E + F .
Notation : Γ ( ⋅ ) denotes the Gamma function .
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How do you know about the substitution ???
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@Santiago Hincapie , Kushal is right. What motivates you to use that substitution?
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First apply the following substitution θ = arctan ( 2 1 ( 2 1 / 4 x − 1 / 8 − x 1 / 8 − x − 1 / 8 − x 1 / 8 2 1 / 4 ) ) It is easy to check that x runs from 0 to 1 and the integral becomes 2 1 3 / 4 2 + 1 ∫ 0 1 x + 1 x − 7 / 8 + x − 5 / 8 d x = 2 1 3 / 4 2 + 1 ∫ 0 ∞ x + 1 x − 7 / 8 d x Then the claim follows by the following formula ∫ 0 ∞ ( 1 + x ) b x a − 1 d x = Γ ( b ) Γ ( a ) Γ ( b − a ) then 2 1 ∫ − π / 2 π / 2 1 − ( 2 − 1 ) 2 sin 2 θ d θ = 2 1 3 / 4 π 2 + 1 Γ ( 8 1 ) Γ ( 8 3 ) and A + B + C + D + E + F = 2 + 1 + 1 3 + 4 + 8 + 3 = 3 1