Let "a", "b" and "с" be sides of the triangle ("с" is the longest side). The triangle will be right if a² + b² = c²
a. 13 35 37
13² + 35² = 1394 and 37² = 1369
1394 ≠ 369
b. 6 9 10
6² + 9² = 117 and 10² = 100
117 ≠ 100
c. 5 12 13
5² + 12² = 169 and 13² = 169
169 = 169 ← right triangle
d. 9 40 42
9² + 40² = 1681 and 42² = 1764
1681 ≠ 1784
The answer is c. 5 12 13
