If tan α =1/7, tan β =1/3, then cos 2α is equal to
If tan α =1/7, tan β =1/3, then cos 2α is equal to
(A) sin 2β
(B) sin 4β
(C) sin 3β
(D) cos 2β
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If tan α =1/7, tan β =1/3, then cos 2α is equal to
(A) sin 2β
(B) sin 4β
(C) sin 3β
(D) cos 2β