Q. 16

# Mark the correct alternative in the following:The value of cos (36o – A) cos (36o + A) + cos (54o + A) cos (54o – A) isA. sin 2 AB. cos 2AC. cos 3AD. sin 3A

cos(54o + A) =sin(36o – A)

cos(54o - A) =sin(36o + A)

cos (36o–A) cos (36o+A)+ sin(36o-A)sin(36o+A)=cos(2A)

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