Câu hỏi 71
Tính tích
$$\left(1-\frac{\cos61^\circ}{\cos1^\circ}\right)\left(1-\frac{\cos62^\circ}{\cos2^\circ}\right)\dots\left(1-\frac{\cos119^\circ}{\cos59^\circ}\right).$$
$$\left(1-\frac{\cos61^\circ}{\cos1^\circ}\right)\left(1-\frac{\cos62^\circ}{\cos2^\circ}\right)\dots\left(1-\frac{\cos119^\circ}{\cos59^\circ}\right).$$