First slide

Multiple and sub- multiple Angles

Question

If $\cos A + \cos B + \cos C = 0$ then $\cos 3 A + \cos 3 B + \cos 3 C$ is equal to

Moderate

A

$\cos A \cos B \cos C$
B

$12 \cos A \cos B \cos C$
C

0
D

$8 \cos^{3} A \cos^{3} B \cos^{3} C$

Solution

We have,
$\begin{array}{l} \cos A + \cos B + \cos C = 0 \\ \cos^{3} A + \cos^{3} B + \cos^{3} C = 3 \cos A \cos B \cos C \end{array}$
$\frac{\cos 3 A + 3 \cos A}{4} + \frac{\cos 3 B + 3 \cos B}{4} + \frac{\cos 3 C + 3 \cos C}{4}$
$\Rightarrow \cos 3 A + \cos 3 B + \cos 3 C = 12 \cos A \cos B \cos C$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App