Verifying Trig Identities

I understand the concept and know the identities, however our teacher offered us more difficult bonus problems and this one threw me for a loop.

The problem is

the square root of (1-sin(theta))/(1+sin(theta)) = 1/(sec(thetha) - tan(theta))

My question is... can you square both sides? I tried that and worked the right side until I got (1-sin^2(theta))/(1+sin^2(theta)) ... which, if I took the square root of, I would get (1-sin(theta))/(1+sin(theta)) however I can't just take the square root of one side.

I really don't know where to go with this problem..

Any help is appreciated!

Also, sorry if it makes no sense when I wrote it out.. if you would like me to write it out as an image so it makes more sense, I can. Thanks!