cos 400 cos 800 cos 1600 = | MATH - FUNDAMENTAL TRIGONOMETRICAL | SolveeIt

cos 40⁰ cos 80⁰ cos 160⁰ =

$\frac{–1}{2}$

$\frac{–1}{4}$

$\frac{–1}{8}$

$\frac{–1}{16}$

Answer

$\frac{–1}{8}$

Explanation

cos (60 – 20) cos (60 + 20). cos (160)

= $\frac{\cos 20^{0}}{\cos 20^{0}}$ × cos (60 – 20) × cos(60 + 20) $0$ × cos (160) $0$

= $\frac{1}{4}$ cos 60 $0$ × cos $\frac{(180–20)^{0}}{\cos 20^{0}}$

Ž = $\frac{1}{4}$ × $\frac{1}{2}$ × $\left( –\frac{\cos 20}{\cos 20} \right)$

= – 1/8

Question: cos 40<sup>0</sup> cos 80<sup>0</sup> cos 160<sup>0</sup> =...