` 2 cos^2 B - 1 = tan^2 A`, then `cosA cosB` = – InterviewSolution

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1.	` 2 cos^2 B - 1 = tan^2 A`, then `cosA cosB` =
Answer» `2cos^2B - 1 = tan^2A` `=>2cos^2B - 1 = sec^2A-1` `=>2cos^2B = sec^2A` `=>2cos^2B = 1/cos^2A` `=>cos^2Acos^2B = 1/2` `=>cosAcosB = +-1/sqrt2`

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