From Förberedande kurs i matematik 1

The side marked x is the hypotenuse in the right-angled triangle and the side of length 16 is the adjacent to the angle of 20°.

By writing the quotient for \displaystyle \cos 20^{\circ}, we obtain the relation

\displaystyle \cos 20^{\circ} = \frac{16}{x}

and this gives

\displaystyle x = \frac{16}{\cos20^{\circ}}\quad ({}\approx 17\textrm{.}0)\,\textrm{.}