Question

सिद्ध कीजिए: $2\cos \dfrac{\pi}{13} \cos \dfrac{9\pi}{13} + \cos \dfrac{3\pi}{13} + \cos \dfrac{5\pi}{13} = 0$

Answer 1

13 cos fhhjjjjjkkkkjjj

Answer 2

Step-by-step explanation:

L.H.S

2 cos π/13 cos 9π/13+ cos 3π/13+ cos 5π/13

=cos( π/13+9π/13)+ cos( π/13-9π/13)+ cos 3π/13 + cos 5π/13

=cos 10π/3 +cos 4π/13 + cos 3π/13 + cos5π/13

=cos(π-3π/13) + cos(π-5π/13) +cos 3π/13+ cos 5π/13

= -cos 3π/13 - cos5π/13 + cos 3π/13+ cos 5π/13

=0= R.H.S