Câu hỏi 65
Chứng minh rằng
$$
\sin10^\circ\cdot\cos20^\circ\cdot\sin30^\circ\cdot\cos40^\circ\cdot\sin50^\circ\cdot\cos60^\circ\cdot\sin70^\circ\cdot\cos80^\circ=\frac1{256}.
$$
$$
\sin10^\circ\cdot\cos20^\circ\cdot\sin30^\circ\cdot\cos40^\circ\cdot\sin50^\circ\cdot\cos60^\circ\cdot\sin70^\circ\cdot\cos80^\circ=\frac1{256}.
$$