Answer:
See below
Explanation:
REMEMBER sec = 1/cos ...so the left side is
[1/cos -1] / [1/cos +1 ]
get common denominator for numerator and denominator
[ (1 -cos) /cos ] / [ (1+cos) / cos ]
now flip the bottom fraction and multiply to get
[(1-cos/cos) ] * [ cos / (1+cos) ] which simplifies to ( the 'cos' term cancels)
(1-cos) / (1+cos) done !