Answer:
AB = √((2 - 1)² + (-5 - (-1))²) = √(1² + (-4)²)
= √(1 + 16) = √17
BC = √((2 - (-2))² + (-5 - (-4))²) = √(4² + (-1)²)
= √(16 + 1) = √17
AC = √((-2 - 1)² + (-4 - (-1))²) = √((-3)² + (-3)²)
= √(9 + 9) = √18 = 3√2
ABC is an isosceles triangle.
AC is the longest side.
M = ((1 + (-2))/2, (-1 + (-4))/2) = (-1/2, -5/2)
= (-.5, -2.5)