Is tan(x + 90) = -cot(x) ?

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- Nov 12th 2013, 08:04 AM #1

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- Nov 12th 2013, 08:46 AM #2

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- Nov 12th 2013, 08:47 AM #3

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- Nov 12th 2013, 11:14 AM #4

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## Re: Is tan(x + 90) = -cot(x)?

$\displaystyle tan(x+90) = -cot(x)$

$\displaystyle \frac{tan(x) + tan(90)}{1-tan(x)tan(90)} = -\frac{1}{tan(x)}$

$\displaystyle tan^2(x) + tan(x)tan(90) = tan(x)tan(90) - 1 $

$\displaystyle tan(x) = \sqrt{-1} $

Then what did I do wrong?

- Nov 12th 2013, 11:32 AM #5

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