First slide

Trigonometric transformations

Question

If $x = \sin \frac{2 π}{7} + \sin \frac{4 π}{7} + \sin \frac{8 π}{7}$ $and y = \cos \frac{2 π}{7} + \cos \frac{4 π}{7} + \cos \frac{8 π}{7}, then x^{2} + y^{2} is$

Moderate

A

1
B

2
C

3
D

4.

Solution

$\begin{array}{l} x^{2} + y^{2} = 3 + 2 (\cos \frac{2 π}{7} + \cos \frac{4 π}{7} + \cos \frac{6 π}{7}) \\ = 3 + 2 (- 1 / 2) = 2 \end{array}$

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