sinα+sinr=sinβ,cosβ+cosr=cosα
=> (sinr)^2+(cosr)^2=1
=> 1+1-2sinasinβ-2cosacosβ=1
=> cos(a-β)=0.5
因为sinα+sinr=sinβ,α,β,r属于(0,π/2),所以β>α
α-β=-60