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I'm new to this site and I'm very happy that I found it. My Pre-cal 2 teacher has been no help to me when it comes to explaining certain steps needed to solve a problem. Overall I'm having a hard time choosing the correct identity needed to solve the problems. However what I do not understand about this particular problem is how to change the denominator.

The question is:

Sec/Tan -Tan/Sec = cosxcotx

I started by expanding sec and tan which gave me (1/cos)/(sin/cos)-(cos/sin)/(1/cos)

but what should I do to change the denominator?