Question

cos 1° cos 2° cos 3° ... cos 180° = ?
(a) −1
(b) 1
(c) 0
(d) $\frac{1}{2}$

Answer 1

$$\begin{gathered} \left(\mathrm{c}\right)0 \\ \cos 1^0\cos 2^0\cos 3^0...\cos {180}^0 \\ =\cos 1^0\cos 2^0\cos 3^0...\cos {90}^0...\cos (180{)}^0 \\ =0[\because \cos 90°=0] \end{gathered}$$