(sin⁡12⁢θ)α+12⁢(cos⁡12⁢θ)β+12⁢Pn(α,β)⁡(cos⁡θ)=π-1⁢22⁢n+α+β+1⁢B⁡(n+α+1,n+β+1)⁢(∑m=0M-1fm⁡(θ)2m⁢(2⁢n+α+β+2)m+O⁡(n-M)),