After a little calculus and lots of algebra I get the expression(adsbygoogle = window.adsbygoogle || []).push({});

cot(2la) = (l^2 - k^2) / (2kl)

it is suggested to simplify with the trig identity

tan(t/2) = sqrt(1 + cot^2(t) ) - cot(t)

when I do so, I get

tan(la) = k/l

notice that we have gone from cot(2la) to tan(la). The text I am reading says

tan(la) = l/k

which I think is wrong. Can someone else please give it a try?

the key step was combining the 1 + cot^2(t) over a common denom.

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# Verify a simplification with trig identity

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