和差角公式cos(a±b)=cosacosb∓sinasinbcos(a \pm b) = cosacosb \mp sinasinb \\cos(a±b)=cosacosb∓sinasinbsin(a±b)=sinacosb±cosasinbsin(a \pm b) = sinacosb \pm cosasinb \\sin(a±b)=sinacosb±cosasinbtan(a±b)=tana