[tex]A(4,5)[/tex]
[tex]B(6,1)[/tex]
[tex]\vec{AB}=(x_{B}-x_{A})\vec{i}+(y_{B}-y_{A})\vec{j}[/tex]
[tex]\vec{AB} = (6 - 4) \vec{i} + (1 - 5) \vec{j}[/tex]
[tex]\vec{AB} = 2 \vec{i} - 4 \vec{j}[/tex]
[tex] |\vec{AB}| = \sqrt{ {2}^{2} + {( -4 )}^{2} } = \sqrt{4 + 16} = \sqrt{20} = 2 \sqrt{5} [/tex]
