原式=(cosa)^2+(-(1/2)cosa-(√3/2)sina)^2+(-(1/2)cosa+(√3/2)sina)^2
=(cosa)^2+(1/2)(cosa)^2+(3/2)(sina)^2
=(3/2)((cosa)^2+(sina)^2)
=3/2
0
原式=(cosa)^2+(-(1/2)cosa-(√3/2)sina)^2+(-(1/2)cosa+(√3/2)sina)^2
=(cosa)^2+(1/2)(cosa)^2+(3/2)(sina)^2
=(3/2)((cosa)^2+(sina)^2)
=3/2