对 cos(0.25pi+a)cos(0.25pi-a)=0.25,cos(0.25pi-a）= sin(0.5pi-(0.25pi-a)）= sin(0.25pi+a) 就有cos(0.25pi+a)*sin(0.25pi+a)=0.25,就有sin(0.5+2a) = 0.5 cos2a=0.5 sina的四次方＋cosa的四次方=(sina*sina+cosa...