An isosceles triangle must have two equal angles.
Also, ANY triangle must have 3 angles that add up to 180 degrees.
If one angle is 80 degrees, there are 2 options:
A) One 80 degree angle, and 2 angles of 50 degrees each
B) Two 80 degree angles, with the 3rd angle being 20 degrees
Only one possibility with one 80 degree angle......