The unit vectors along the coordinate axes are called the standard unit vectors. They are denoted by [math]i^{\rightarrow},j^{\rightarrow},k^{\rightarrow}[/math] acting along X-, Y- and Z- axes respectively as shown in the figure.

In terms of coordinates [math]i^{\rightarrow}=\left(1,0,0\right)[/math],[math]j^{\rightarrow}=\left(0,1,0\right)[/math] and [math]k^{\rightarrow}=\left(0,0,1\right)[/math]. In case of plane vectors, [math]i^{\rightarrow}=\left(1,0\right)[/math] and [math]j^{\rightarrow}=\left(0,1\right)[/math]. There will be no unit vector along the Z-axis.

(i) Every plane vector is of the form a[sub]1[math]i^{\rightarrow}[/math][/sub]+b[sub]1[math]j^{\rightarrow}[/math][/sub] and conversely.[br](ii) Every space vector is of the form a[sub]1[math]i^{\rightarrow}[/math][/sub]+b[sub]1[math]j^{\rightarrow}[/math][/sub]+c[sub]1[math]k^{\rightarrow}[/math][/sub][br]