两角和与差： cos(+B)=cosa cosB-sinasinB cos(-B)=cosa cosB+sinasinB sin(+B)=sina cosB+cosasinB sin(a-B)=sina cos B-cosasin B cos cos cos sin sin (      + = − ) cos cos cos sin sin (      − = + ) sin sin cos cos sin (      + = + ) sin sin cos cos sin (      − = − ) 两角和与差：