cos left(frac{2 pi}{7}right)+cos left(frac{4 | vedclass

Name: PDF Generator App | JEE NEET Paper Generator | Vedclass
Brand: Vedclass
Rating: 5 (35 reviews)

Question

$\cos \frac{2 \pi}{7}+\cos \frac{4 \pi}{7}+\cos \frac{6 \pi}{7}$

$=\frac{\sin \left(3 	imes \frac{\pi}{7}ight)}{\sin \frac{\pi}{7}} 	imes \cos

Vedclass · Accepted Answer

$-\frac{1}{2}$

Vedclass · Answer

$\cos \frac{2 \pi}{7}+\cos \frac{4 \pi}{7}+\cos \frac{6 \pi}{7}$

$=\frac{\sin \left(3 	imes \frac{\pi}{7}ight)}{\sin \frac{\pi}{7}} 	imes \cos \left(\frac{\frac{2 \pi}{7}+\frac{6 \pi}{7}}{2}ight)$

$=\frac{2 \sin \left(\frac{3 \pi}{7}ight)}{2 \sin \frac{\pi}{7}} 	imes \cos \left(\frac{4 \pi}{7}ight)$

$=\frac{\sin \left(\frac{7 \pi}{7}ight)+\sin \left(\frac{-\pi}{7}ight)}{2 \sin \frac{\pi}{7}}$

$=\frac{-\sin \frac{\pi}{7}}{2 \sin \frac{\pi}{7}}$

$=-\frac{1}{2}$

$\cos \left(\frac{2 \pi}{7}\right)+\cos \left(\frac{4 \pi}{7}\right)+\cos \left(\frac{6 \pi}{7}\right)$ ની કિંમત $\dots\dots$છે.

Similar Questions

જો $A = 580^o$ હોય તો નીચેનામાંથી ક્યું સાચું છે ?

જો $A, B, C$ એ ત્રણ ખૂણા છે કે જેથી $sinA + sinB + sinC = 0,$ થાય તો

$ \frac {sinAsin BsinC}{(sin 3A+ sin 3B+ sin 3C)}$ (wherever definied)=

સાબિત કરો કે : $\cot x \cot 2 x-\cot 2 x \cot 3 x-\cot 3 x \cot x=1$

જો $\frac{\sqrt{2} \sin \alpha}{\sqrt{1+\cos 2 \alpha}}=\frac{1}{7}$ અને $\sqrt{\frac{1-\cos 2 \beta}{2}}=\frac{1}{\sqrt{10}}$ $\alpha, \beta \in\left(0, \frac{\pi}{2}\right),$ તો $\tan (\alpha+2 \beta)$ મેળવો.

જો $x = \cos 10^\circ \cos 20^\circ \cos 40^\circ ,$ તો $x =.....$