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Evaluate the following: cos 80^0cos 20^0...

Evaluate the following: `cos 80^0cos 20^0+ sin 80^0 sin 20^0`

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Given,L.H.S= `cos 80^ocos 20^o+ sin 80^o sin 20^o`
=`cos(80^o-20^o)`
=`cos(60^o)`
=`1/2`
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