Question

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

Answer 1

$$\begin{gathered} \cos 1°\cos 2°\cos 3°......\cos 180° \\ =\cos 1°\cos 2°\cos 3°......\cos 90°......\cos 180° \\ =\cos 1°\cos 2°\cos 3°......\times 0\times ......\cos 180°\left(\because \cos 90°=0\right) \\ =0 \\ \mathrm{Hence},\mathrm{the}\mathrm{correct}\mathrm{option}\mathrm{is}\left(\mathrm{a}\right). \end{gathered}$$