Part 1
Using the distance formula,
So, the measure of the longest side is 6 units.
Part 2
Triangle ABD will have vertices A(1,7), B(-2, 2), and D(1,2).
We already know that
Using the distance formula,
So, ABD is a scalene triangle.
Part 3
From part 2, we know that the length of side AD is 5 units.