From Förberedande kurs i matematik 1

The opposite and adjacent are given in the right-angled triangle and this means that the value of the tangent for the angle can be determined as the quotient between the opposite and the adjacent:

\displaystyle \text{tan }v\text{ }={2}/{5}\;~

At the same time, this is a trigonometric equation for the angle \displaystyle v.

NOTE: In the chapter on "Trigonometric equations", we will investigate more closely how to solve equations of this type.