Are the sides to a triangle 20 40 80 cm a right angle?

To test if a triangle in right angled. apply Pythagorean Formula

H^(2) = s^(2) + S^(2)

H is the hypotenuse and will always be the longest side.

Hence

for a 20, 40 , 80 triangle.

H ; 80^(2) = 6400

s^(2) + S^(2) [ 20^(2) + 40^(2) = 400 + 1600 = 2000

2000 is NOT equal to 6400. Hence for the given dimensions it is NOT a Right-Angled triangle.