Checkout JEE MAINS 2022 Question Paper Analysis : Checkout JEE MAINS 2022 Question Paper Analysis :

The expression cos 10π/13 + cos 8π/13 + cos 3π/13 + cos 5π/13 is

The expression cos 10π/13 + cos 8π/13 + cos 3π/13 + cos 5π/13 is

1) – 1

2) 0

3) 1

4) None of these

Answer: (2) 0

Solution:

cos 10π/13 + cos 8π/13 + cos 3π/13 + cos 5π/13

cos(π – 3π/13) + cos(π – 5π/13) + cos 3π/13 + cos 5π/13 {since cos (π – A) = -cos A}

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

= 0

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