Answer:
There is an error in the question.
All angles in an equilateral triange are 60º
I just used my Ti 84
it is correct except for 3rd number
should be
-3
-6
-16
8
The formula of a slope:

We have the points A(-7, a) and B(c, d).
Substitute:

Exception: c ≠ -7.
Which ones do you need help on?
AB = BE = 5
BD = BE + ED = 5 + 3 = 8
BC = 8
BD = BC
CD = 5 which is not equal to 8.
Triangle BCD has exactly 2 congruent sides.
Answer: Triangle BCD is isosceles.