Question 137400
tanvsinv/tanv+sinv=tanv-sinv/tanvsinv

Cross-multiply to get: 
(tan*sin^2 = tan^2-sin^2

Divide thru by sin2 to get:

tan^2 = sec^2 -1

This is a pythagorean identity:

tan^2 = tan^2
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Cheers,
Stan H.