If cos α+cos β=0=sin α+sin β, then prove that cos 2α+cos 2β=−2 – InterviewSolution

1.	If cos α+cos β=0=sin α+sin β, then prove that cos 2α+cos 2β=−2 cos (α+β)
Answer» If $c o s α + c o s β = 0 = s i n α + s i n β$ , then prove that $c o s 2 α + c o s 2 β = - 2 c o s (α + β)$

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