I=∫a0ln(cot a+tan x)dx, where aϵ(0,π2), then I is equal to
–aln(sina)
I=∫a0ln(cot a+tan x)dx
=∫a0ln(cos(a−x)sin a cos x)dx ...(1)
∴I=∫a0ln(cos xsin a cos (a−x))dx ...(2)
Adding (1) and (2) we get 2I=∫a0ln(1sin2a)dx
2I=−2∫a0ln(sin a)dx
I=−a ln (sin a)