sinα+sinβ=3/5,则(sinα+sinβ)^2=9/25,即(sinα)^2+(sinβ)^2+2sinαsinβ=9/25,同理cosα+cosβ=4/5,则(cosα+cosβ)^2=16/25,即(cosα)^2+(cosβ)^2+2cosαcosβ=16/25两式相加(sinα)^2+(cosα)^2+(sinβ)^2+(...