Question

Sin a Sin a
____ - _____
1-cos a 1+ cos a

Answer 1

$frac{sin alpha }{1-cos alpha } - frac{sin alpha }{1+cos alpha } = frac{sin alpha (1+cos alpha )-sin alpha (1-cos alpha )}{(1-cos alpha )(1+cos alpha )} =$
$frac{sin alpha +sin alpha cos alpha -sin alpha +sin alpha cos alpha }{1- cos alpha ^{2} }= frac{2*sin alpha *cos alpha }{sin alpha ^{2} } =2ctg$