∫_{₀}^{2π }cosh( k a sinθ) sin( k a cosθ) cosθ dθ = πka (how to prove that step by step)???????

where π = pi

∫_{₀}^{2π}= integration from zero to 2π

the book i am reading got mentioned that ; on expanding the cosh and cosine terms, four separate integrals may be obtained. from symmetry it may be shown that three of these integrals are identically zero leaving...