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posted by Blaire on Sunday, March 2, 2014 at 6:29pm.
Prove: [(tan^2theta+1)(cos^2theta-1)]=1-sec^2theta
tan^2 = sin^2/cos^2 = s^2/c^2 (s^2/c^2+1)(c^2-1) = s^2 -s^2/c^2 +c^2 -1 but s^2 + c^2 = 1 so we have -s^2/c^2 = -(1 - c^2)/c^2 = - 1/c^2 + 1 = 1 - sec^2
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