cos x/(1+sin x) + cos x/(1-sin x) = [cos x(1-sin x) + cos x(1+sin x)]/ [(1+sin x)(1- sin x)] = [cos x - cos x.sin x + cos x + cos x.sin x]/[1- sin^2 x] ( sin^2 + cos^2 =1) = 2cos x/cos ^2 x =2/cos x ( cos x = 1/sec x) = 2 sec x

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Jan 25th, 2015

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