sin 11пи/2=?
cos (-13пи/4)=?
sin 7пи/3=?
cos (-13пи/6)=?

sin(6π-π/2)=sin(-π/2)=-1cos(-13π/4)=cos(13π/4)=cos(3π+π/4)=cos(π+π/4)=-cosπ/4=-√2/2sin(2π+π/3)=sinπ/3=√3/2cos(-13π/6)=cos(13π/6)=cos(2π+π/6)=cos(π/6)=√3/2