## Precalculus (6th Edition) Blitzer

If ${{\mathbf{F}}_{1}}$ and ${{\mathbf{F}}_{2}}$ are two forces acting on an object, the vector sum ${{\mathbf{F}}_{1}}+{{\mathbf{F}}_{2}}$ is called the resultant force.
The algebraic addition of vectors $\mathbf{a}$, $\mathbf{b}$, $\mathbf{c}$, and $\mathbf{d}$ etc. is called vector addition, and it is equal to the resultant of all the vectors. In the same manner, ${{\mathbf{F}}_{1}}$ and ${{\mathbf{F}}_{2}}$ are also the two vectors; therefore the vector sum ${{\mathbf{F}}_{1}}+{{\mathbf{F}}_{2}}$ is called the resultant force.