sec θ / [ csc θ - cot θ ] - sec θ / [ csc θ + cot θ] get a common denominator
[ sec θ (csc θ + cot θ) - sec θ ( csc θ - cot θ ] / [ csc^2 θ - cot^2 θ ]
[ 2sec θ cot θ ] / 1
[ 2 ( 1 / cos θ) (cos θ / sin θ) ]
[ 2 / sin θ ]
2 csc θ and this = the right side
