A given triangle to be right-angled, if it satisfies Pythagorean Theorem. That is, the sum of the squares of the two smaller sides must be equal to the square of the largest side.
1.6 cm, 3.8 cm, 4 cm
Longest side = 4 cm
(4)2 = 16
and (1.6)2 + (3.8)2 = 2.56 + 14.44 = 17.00 = 17
16 ≠ 17
It is not a right triangle.
