Proposed:
∫π/40√sin(2x)cos2(x)dx=2−√2π⋅Γ2(34)
My try:
Change (1) to
∫π/40√2sec2(x)tan(x)dx
∫π/40√2tan(x)+2tan3(x)dx
Not sure what substitution to use
How may we prove (1)?
Answer
By substituting x=arctant our integral takes the form:
I=∫10√2t1+t2dt
and by substituting 2t1+t2=u we get:
I=∫10(−1+1√1−u2)duu3/2
that is straightforward to compute through the substitution u2=s and Euler's Beta function:
I=12(4+√πΓ(−14)Γ(14)).
The identities Γ(z+1)=zΓ(z) and Γ(z)Γ(1−z)=πsin(πz) settle OP's (1).
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