(N/A) Subtraction of vectors can be defined in terms of the addition of vectors.
We define the difference of two vectors $\overrightarrow{A}$ and $\overrightarrow{B}$ as the sum of two vectors $\overrightarrow{A}$ and $-\overrightarrow{B}$.
$\overrightarrow{A} - \overrightarrow{B} = \overrightarrow{A} + (-\overrightarrow{B})$
Thus,the subtraction of vectors means adding the opposite of a vector to another vector.
In figure $(a)$,$\vec{A}$,$\vec{B}$,and $-\vec{B}$ are represented.
In figure $(b)$,$-\vec{B}$ is added to $\vec{A}$.
By the triangle method for vector addition,
$\overrightarrow{R_{2}} = \overrightarrow{A} + (-\overrightarrow{B})$
$\therefore \overrightarrow{R_{2}} = \overrightarrow{A} - \overrightarrow{B}$
(For comparison,$\overrightarrow{R_{1}} = \overrightarrow{A} + \overrightarrow{B}$ is shown).