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Prove that tanA+tanC=b^2 / ac

Ok so far i've got that tan A= a/c and tanC=c/a and then when i try to add those together i get (c^2)(a^2)/ac , but how can (c^2)(a^2) = b^2

all I've thought of is pythagorus's theorem. But for it to equal b^2, a^2 has to be taken away from c^2

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# Trigonometry help

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