====================================================
Explanation:
The two points given are
C = (x1,y1) = (2,-1)
D = (x2,y2) = (5,3)
Use the distance formula
[tex]d = \sqrt{(x_1 - x_2)^2 + (y_1 - y_2)^2}\\\\d = \sqrt{(2-5)^2 + (-1-3)^2}\\\\d = \sqrt{(-3)^2 + (-4)^2}\\\\d = \sqrt{9 + 16}\\\\d = \sqrt{25}\\\\d = 5\\\\[/tex]
The distance from C to D is 5 units. This is the same as saying segment CD is 5 units long.