you need to use the distance formula
[tex]d = \sqrt{ {(x - x)}^{2} + {(y - y)}^{2} } [/tex]
[tex] \sqrt{ {(5 + 3)}^{2} + {( - 2 - 8)}^{2} } [/tex]
so the distance between points (5,-2) and (-3,8) is
[tex]2 \sqrt{41} [/tex]
which won't simplify so it stays as is