Answer:
Let A = (5, -1) (x1, y1)
Let B = (10, -1) (x2, y2)
Length AB =
[tex] = \sqrt{ {(x2 - x1)}^{2} + {(y2 - y1)}^{2} } [/tex]
[tex] = \sqrt{ {(10 - 5)}^{2} + {( - 1 + ( - 1))}^{2} } [/tex]
[tex] \\ = \sqrt{ {(5)}^{2} + {( - 2)}^{2} } [/tex]
[tex] = √25 - 4[/tex]
[tex] = √21[/tex]