User talk:U Han Zin

Derivation of cos(θ+Δθ) and sin(θ+Δθ).
cos(θ+Δθ),sin(θ+Δθ)=x(cosθ,sinθ)+y(-sinθ,cosθ) =(x,y)(cosθ,-sinθ),(x,y)(sinθ,cosθ) =xcosθ-ysinθ,xsinθ+ycosθ Substitution x=cosΔθ,y=sinΔθ, =cosΔθcosθ-sinΔθsinθ,cosΔθsinθ+sinΔθcosθ