Question

若cos（a-b)=1/3,则(sina+sinb)^2+(cosa+cosb)^2=

Answer 1

(sina+sinb)^2+(cosa+cosb)^2=

(sina)^2+(sinb)^2+2(sina)(sinb)+(cosa)^2+(cosb)^2+2(cosa)(cosb)=

2+2[(sina)(sinb)+(cosa)(cosb)]=

2+2cos（a-b)=8/3