Definition:Vector Sum/Triangle Law

Definition
Let $\mathbf u$ and $\mathbf v$ be vector quantities of the same physical property. Let $\mathbf u$ and $\mathbf v$ be represented by arrows embedded in the plane such that:


 * $\mathbf u$ is represented by $\vec {AB}$
 * $\mathbf v$ is represented by $\vec {BC}$

that is, so that the initial point of $\mathbf v$ is identified with the terminal point of $\mathbf u$.


 * Vector-sum-triangle-law.png

Then their (vector) sum $\mathbf u + \mathbf v$ is represented by the arrow $\vec {AC}$.