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# Given cos(A−B)=cosAcosB+sinAsinB. Taking suitable A and B, find cos15∘.

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#### We have,cos(A−B)=cosAcosB+sinAsinB …… (1)Then, cos15o=?Let A=45o and B=30oPut the value of A and B in equation (1) and we get,cos(45o−30o)=cos45ocos30o+sin45osin30ocos15o=1√2×√32+1√2×12cos15o=√3+12√2Hence, this is the answer.

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