Answer :

Given to find the value for,


cos2 76o + cos2 16o – cos 76o cos 16o


In the above expression consider cos 76o cos 16o


[By using the trigonometric sum formula, we can say that,


cos(C+D) + cos ( C-D) = 2 cos C cos D]


Now multiply and divide this with 2, we get




Consider the full expression,





Multiplying and dividing the terms cos2 76° + cos2 16° with 2




[ by using the formula, cos 2θ = 2cos2θ – 1 2cos2θ = cos 2θ +1 ]



[ by using the formula, cos A + cos B ]







Hence, cos2 76o + cos2 16o – cos 76o cos 16o


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