With respect to a rectangular cartesian coordinate system, three vectors are expressed as

$\overrightarrow{\mathrm{a}}=4\widehat{\mathrm{i}}-\widehat{\mathrm{j}}$, $\overrightarrow{\mathrm{b}}=-3\widehat{\mathrm{i}}+2\widehat{\mathrm{j}}$ and $\overrightarrow{\mathrm{c}}\mathrm{\hspace{0.17em}}=-\widehat{\mathrm{k}}$

where $\widehat{\mathrm{i}},\widehat{\mathrm{j}},\widehat{\mathrm{k}}$ are unit vectors, along the X, Y and Z-axis respectively. The unit vector along the direction of sum of these vector is