sina+sinβ=1(sina+sinβ)^2=1(sina)^2+(sinβ)^2+2sinasinβ≥4sinasinβ所以sinasinβ≤1/4(cosa+cosβ)^2=(cosa)^2+(cosβ)^2+2cosacosβ≤2[(cosa)^2+(cosβ)^2]=2[2-(sina)^2-(sinβ)^2]=2[2-(sina+sinβ)^2+2s...