What is the area, in square units, of the square with the four vertices at $A\ (0, 0)$, $B\ (-5, -1)$, $C\ (-4, -6)$ and $D\ (1, -5)$?
Easy! The area of the square is 18.
That is wrong
Use Pythagoras to get the length of one side, then square it to get the area.