Question

find the value of cos 15°​

Answer 1

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$we\:know\:that,$

$cos(a-b)=cos a × cos b+ sin a × sin b$

$cos 15°= cos (45°-30°)$

$cos15°=cos45°×cos30°+sin45°×sin 30°$

$cos 15°= (\frac{1}{\sqrt{2}})× (\frac{ \sqrt{3}}{2}) + (\frac{1}{ \sqrt{2}})×\frac{1}{2}$

$cos 15°= ({ \sqrt{3}}+ 1 )/(2{ \sqrt{2}})$

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