Coordinates in geometry: similarity w/ (0, 7), (2, 0), (0, −14), (−4, 0), & origin

[Matilda]

Coordinates in geometry: similarity w/ (0, 7), (2, 0), (0, −14), (−4, 0), & origin

1. Show that ΔOAB and ΔOCD are similar where (0, 7), (2, 0), (0, −14)and (−4, 0) are the points A, B, Cand D respectively and O is the origin.
   
   I've solved to show that 2 pairs of sides are in proportion but I can't seem to get the last step in proving they are similar. The answers show that +AOB = +COD = 90°. How do I figure that out though?

 

[Deleted member 4993]

1. Show that ΔOAB and ΔOCD are similar where (0, 7), (2, 0), (0, −14)and (−4, 0) are the points A, B, Cand D respectively and O is the origin.
   
   I've solved to show that 2 pairs of sides are in proportion but I can't seem to get the last step in proving they are similar. The answers show that +AOB = +COD = 90°. How do I figure that out though?

A is y-axis and B is on x-axis - what do you think AOB should be where O is the origin?