This is my work so far for proving this trig identity. What should I do next? Is there anything I did wrong thus far?

cotx=tan(-(x-pi/2))

Right side:

tan(-x+pi/2)

[-tanx+tanpi/2]/[1-(-tanx)(tanpi/2)]

[-sinx/cosx+tanpi/2]/[1+(sinx/cosx)(tanpi/2)]

also, tanpi/2 is undefined... what does that do to the question?

thank you in advance!