Math problem in Huygens-Fresnel principle

[mensa]

in Huygens-Fresnel principle, U(P)=K*∫∫U(Q)*F(θ0，θ0)*exp{ikr}/r*d∑
K=-i/λ; F(θ0，θ0)=0.5(cosθ0+cosθ) is inclination factor; d∑ is a small part of any close surfaces; these are all include in any Beam Optics book

I want to demonstrate the spherical wave point source S gives out, all the d∑ in the spherical surface as Secondary Source, whose light come to point P, equals to S only

I don't know how to integrate,coz it seems to hard to me.
Please show the process. Any book involves is available too.Thanks

 

[mensa]

I'm so confused that no one could give me any answer...Is it because I didn't get the idea through? Please let me know...thx

 

[ftfaaa]

I can't understand the formula U(P)=K*∫∫U(Q)*F(θ0，θ0)*exp{ikr}/r*d∑.
Can you express it more clearly?