a teacher wrote on the board(adsbygoogle = window.adsbygoogle || []).push({});

tan-1(a) + tan-1(b) + tan-1(c) = pi

[they are inverse trig functions btw, not the recipricol 1/tanx = cotx]

hence prove that

a + b + c = abc

wow. do you have any idea where i can start? thanks. i've been uttered clueless.

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# Trig proof

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