Respuesta :

for a triangle to be right angled  the largest side  squared must equal the sum of the squares on the other 2 sides ( Pythagoras theorem)

1.   101^2 = 99^2 + 20^2   so its is right angled

2. 28^2  is not equal to 26^2 + 12^2  - not right angled

3.  17^2 not euql to 14^2 + 6^2 - not 

First one 101, 99 and 20