Aus Online Mathematik Brückenkurs 1

The side adjacent to the angle of 50° is marked x and the opposite is the side of length 19.

If we write the tangent for the angle, this gives a relation which contains x as the only unknown,

\displaystyle \tan 50^{\circ} = \frac{19}{x}\,\textrm{.}

This gives

\displaystyle x=\frac{19}{\tan 50^{\circ }}\quad ({}\approx 15\textrm{.}9)\,\textrm{.}