Question 176514

 ((sin(a))/(1+sin(a))) - ((sin(a))/(1-sin(a))

least common denominator: (1+sin(a))(1-sin(a)) = 1- sin^2(a) = cos^2(a)

Rewrite each fraction with lcd as its denominator:

= [(sin(a))(1- sin(a)]/lcd - [(sin(a))(1 + sin(a))]/lcd

Combine the humerators over the lcd:

= [sin(a) - sin^2(a) - sin(a) -sin^2(a)]/cd

= [-2sin^2(a)]/lcd

= [-2sin^2(a)]/cos^2(a) = -2tan^2(a)
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Cheers,
Stan H.