Answer:
√20 units
Step-by-step explanation:
[tex]Solution,\\\\\hookrightarrow Here,\\\\\hookrightarrow Coordinate\:of\::\\\\\hookrightarrow A(4,5),B(2,1),C(4,1)\\\\Now,\\\\Let,\\\\(x_1,y_1)=(4,5)\\\\(x_2,y_2)=(2,1)\\\\Using\:distance\:formula\\\\Distance\:of\:AB=\sqrt{(x_2-x_1)^{2}+(y_2-y_1)^{2}} \\\\Distance\:of\:AB=\sqrt{(2-4)^{2}+(1-5)^{2}} \\\\Distance\:of\:AB=\sqrt{(2-4)^{2}+(1-5)^{2}} \\\\Distance\:of\:AB=\sqrt{(-2)^{2}+(-4)^{2}} \\\\Distance\:of\:AB=\sqrt{4+16} \\\\Distance\:of\:AB=\sqrt{20}\: units[/tex]