Question #4d1cc

1 Answer
Nghi N.
Feb 16, 2017

Develop the left side:
LS = cos u/(1 - sin u/(cos u)) + sin u/(1 - cos u/(sin u)) =
= cos^2 u/(cos u - sin u) - sin^2 u/(cos u - sin u) =
= (cos^2 u - sin^2 u)/(cos u - sin u) =
= [(cos u - sin u)(cos u + sin u)]/(cos u - sin u) = cos u + sin u#

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