Some definitions are important for angle measurements such as right, obtuse, and acute angles. In this post we are going to talk about these concepts. Adjacent supplementary angle Definition: Given a ray $\overrightarrow{oa}$ and an opposite ray $\overrightarrow{oc}$. We project a ray $\overrightarrow{ob}$ at a point in the plane. We say that the angle formed by points $b\hat{o}c$ is supplementary (supplement) and adjacent (neighbor) to the angle formed by points $a\hat{o}b$.