Posted by rossi on Friday, November 26, 2010 at 4:35pm.
sin (a+b) = sin a cos b + cos a sin b
sin (a-b) = sin a cos b - cos a sin b
product
sin^2 a cos^2 b - cos^2 a sin^2 b
now divide by cos^2 a cos^2 b
sin^2 a/cos^2a - sin^2 b/ cos^2 b
= tan^2 a - tan^2 b
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