How do you prove #tan2A - 2tanAsin^2A = sin2A#?

1 Answer
KillerBunny
Nov 28, 2015

You can't prove it, since it's not true!

Explanation:

Are you sure that you copied correctly? It doesn't look like an identity, check the graphs of the left and right member:

Left member, right member.

Also, it's hard to believe that the two terms are equal, because one ranges from #-infty# to #infty# (since the tangent does), while the other is bounded between #-1# and #1#.

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