Answer:
Option B is the right option
solution,
A(4,5)------->(X1,x2)
B(2,1)-------->(y1,y2)
Now,
[tex]ab = \sqrt{ {(x2 - x1)}^{2} + {(y2 - y1)}^{2} } \\ \: \: \: = \sqrt{ {(2 - 4)}^{2} + {(1 - 5)}^{2} } \\ \: \: = \sqrt{ {( - 2)}^{2} + {( - 4)}^{2} } \\ \: \: = \sqrt{4 + 16} \\ \: \: \ = \sqrt{20} [/tex]
hope this helps....
Good luck on your assignment..