If the triangles are right triangles then Pythagoras' Theorem will apply: c^2 = a^2 + b^2
I. 1^2 = 0.6^2 + 0.8^2
1 = 0.36 + 0.64
1 = 1 is true therefor I is a right triangle
II. 13^2 = 7^2 + 7^2
169 = 49 + 49
169 is not equal to 98, therefor II is not a right triangle
III. (5/13)^2 = (3/13)^2 + (4/13)^2
25/169 = 9/169 + 16/169
25/169 = 25/169 therefor III is a right triangle
Therefor the answers are A and C
