1+cos 10^{circ}+cos 20^{circ}+cos 30^{circ}= | vedclass

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Question

(B) We have,$1+\cos 10^{\circ}+\cos 20^{\circ}+\cos 30^{\circ} = (1+\cos 10^{\circ}) + (\cos 20^{\circ}+\cos 30^{\circ})$ $= 2\cos^2 5^{\circ} + 2\cos

Vedclass · Accepted Answer

$4 \cos 5^{\circ} \cos 10^{\circ} \cos 15^{\circ}$

Vedclass · Answer

(B) We have,$1+\cos 10^{\circ}+\cos 20^{\circ}+\cos 30^{\circ} = (1+\cos 10^{\circ}) + (\cos 20^{\circ}+\cos 30^{\circ})$ $= 2\cos^2 5^{\circ} + 2\cos 25^{\circ} \cos 5^{\circ}$ $= 2\cos 5^{\circ} (\cos 5^{\circ} + \cos 25^{\circ})$ $= 2\cos 5^{\circ} (2\cos \frac{25^{\circ}+5^{\circ}}{2} \cos \frac{25^{\circ}-5^{\circ}}{2})$ $= 2\cos 5^{\circ} (2\cos 15^{\circ} \cos 10^{\circ})$ $= 4\cos 5^{\circ} \cos 10^{\circ} \cos 15^{\circ}$

$1+\cos 10^{\circ}+\cos 20^{\circ}+\cos 30^{\circ}=$

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