The value of ${\cos ^3}\left( {{\pi \over 8}} \right)$${\cos}\left( {{3\pi \over 8}} \right)$+${\sin ^3}\left( {{\pi \over 8}} \right)$${\sin}\left( {{3\pi \over 8}} \right)$ is :

Question

The value of
${\cos ^3}\left( {{\pi \over 8}} \right)$${\cos}\left( {{3\pi \over 8}} \right)$+${\sin ^3}\left( {{\pi \over 8}} \right)$${\sin}\left( {{3\pi \over 8}} \right)$
is :

${1 \over {\sqrt 2 }}$

${1 \over 2}$

${1 \over 4}$

${1 \over 2{\sqrt 2 }}$

Solution

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