When trying to figure out if three sides or angles make a triangle, here’s some notes:
-The sum of the length of every two sides must exceed the length of the third side. So simply calculate two of the shorter sides. The two sides must be longer than the third side.
-For angles, simply add all three angles. A triangle must have 180 degrees.
The first one (72cm, 17cm, 54cm) is not a triangle because 17+54 does not exceed 72.
The second one (18in, 18in, 32in) is a obtuse isosceles triangle.
The third one (38 degrees, 57 degrees, 80 degrees) is not a triangle because they do not add up to 180.