حاصل $\sin ({۱۵۰^ \circ }) + \cos ({۲۱۰^ \circ })$ کدام است؟
$\sin ({150^ \circ }) = \sin ({180^ \circ } - {30^ \circ }) = \sin {30^ \circ } = \frac{1}{2}$ $\cos ({210^ \circ }) = \cos ({180^ \circ } + {30^ \circ }) = - \cos {30^ \circ } = - \frac{{\sqrt 3 }}{2}$ $ = \frac{1}{2} - \frac{{\sqrt 3 }}{2} = \frac{{1 - \sqrt 3 }}{2}$