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posted by Adam on Tuesday, March 2, 2010 at 11:37pm.

prove cos squared B- sin squared B= 2cos squared B -1

cos^2 B - sin^2 B = 2cos^ B - 1 LS = cos^2 B - (1 - cos^2 B) = 2cos^2 B - 1 = RS

substitute 1 - cos^2B for sin^2 B

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