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Home  >>  JEEMAIN and AIPMT  >>  Mathematics  >>  Trignometry
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Find $\cos 55^{\large\circ}+\cos 65^{\large \circ}+\cos 175^{\large\circ}$


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$\Rightarrow 2\cos 60^{\large\circ}\cos(-5)^{\large\circ}+\cos 175^{\large\circ}$
$\Rightarrow 2\times\large\frac{1}{2}.$$\cos 5^{\large\circ}+\cos(180^{\large\circ}-5^{\large\circ})$
$\Rightarrow \cos 5^{\large\circ}-\cos 5^{\large\circ}$
$\Rightarrow 0$
Hence (a) is the correct answer.
answered Oct 9, 2013 by sreemathi.v

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