The point where the two axes intersect (0,0) it's the point of origin.
Essentially, what we need to do here is prove that BE=EC, BE=CB, and.or CE=BC therefore making it isosceles. With ∠AEC=∠DEB, we know AE=DE, so EC=EB (the points go in order). Therefore, as EC=EB, BEC is isosceles (it has at least 2 equal sides).
Feel free to ask further questions!
14. sometimes, you can have a 45-45-90 or 60-30-90 triangle (degrees)
sometimes true
15. always
16. never, paralellogram has 2 pairs of paralell sides, trapezoid has 1
17.always
18. sometimes
19. always
20. always
