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This probably seems like a very basic question but it has been along time since I did any trigonometry...

I am trying to calculate the sides of an obtuse triangle given the 3 angles:

$$\angle A = 38.6642, \angle B = 136.56, \angle C = 4.775$$

and the side $a = 10.18$ (opposite $\angle A$).

I have tried the Sine Rule:

$$\frac{a}{\sin(A)} = \frac{b}{\sin(B)} = \frac{c}{\sin(C)}$$

thus yielding

$c = \sin(C) \cdot \dfrac{a}{\sin(A)}$ , but with the triangle I have, that gives me $-12.3948...$

What have I misunderstood? How can I calculate the sides?

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    $\begingroup$ What are you using for $\sin(A)$ and $\sin(C)$? Calculators have different modes for degrees and radians; software (such as spreasheets) often requires radians. $\endgroup$ – David K Mar 20 '17 at 17:38
  • $\begingroup$ I am using MATLAB. Turns out the sin() function requires radians, a silly mistake, thanks for helping! To convert degrees to radians the degtorad() function can be used. $\endgroup$ – Samuel Barnes Mar 20 '17 at 17:43
  • $\begingroup$ Type \sin x, \cos x, \tan x, \csc x, \sec x, and \cot x, respectively, when you are in math mode to obtain $\sin x$, $\cos x$, $\tan x$, $\csc x$, $\sec x$, and $\cot x$. See this tutorial on how to typeset mathematics on this site. $\endgroup$ – N. F. Taussig Mar 24 '17 at 22:04
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I was using MATLAB and the sin() function requires radians. To convert degrees to radians the degtorad() function can be used.

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  • $\begingroup$ Or sind, cosd, etc. $\endgroup$ – horchler Mar 20 '17 at 23:18

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