Cos 1° + cos 2° + cos 3° + ..... + cos 180° =

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3.Trigonometrical Ratios, Functions and Identities

easy

$\cos 1^\circ + \cos 2^\circ + \cos 3^\circ + ..... + \cos 180^\circ = $

A

$0$

B

$1$

C

$-1$

D

$2$

Solution

$(\cos 1^\circ + \cos 179^\circ ) + (\cos 2^\circ + \cos 178^\circ ) + ….$

$ + (\cos 89^\circ + \cos 91^\circ ) + \cos 90^\circ + \cos 180^\circ = – 1$.

Standard 11

Mathematics

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