You can put this solution on YOUR website! prove the identity: (1-tan'squared'a)/(1+tan'squared'a)= cos'squared'a-sin'squared'a
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(1-tan^2(a))/(1+tan^2(a))
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(1-(sin/cos)^2)/(1+sin/cos)^2)
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[(cos^2-sin^2)/cos^2)]/[(cos^2+sin^2)/cos^2)]
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Invert the denominator and multiply to get:
[(cos^2-sin^2)/cos^2)]/[cos^2/(cos^2+sin^2)]
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Cancel the cos^2 factors and convert cos^2+sin^2 to 1 to get:
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= cos^2-sin^2
Which is the right side of your original problem.
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Cheers,
Stan H.
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