已知0
cos(被他-丌/4)=1/3 sin(被他-丌/4)=2√2/3 sin(a+被他)=4/5 cos(a+被他)=-3/5sin(a+丌/4)=sin[(a+被他)+(被他-丌/4)=sin(a+被他)cos(被他-丌/4)+cos(a+被他)sin(被他-丌/4)=4/5*1/3-3/5*2√2/3=(4-6√2)/15