Okay onto the problem. I have to prove both sides are the same. So I gotta make one side look exactly like the other using trig identities and algebra. The thing is you can only work one side you have to leave the other alone.
1+TanATan2A=TanACotA-1
1+TanATan2A=TanACotA-1
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just use tan 2a = 2 tan a / [ 1 - tan² a] on both sides and it falls right out