1)
8² + 15² = 17²
64 + 225 = 289
This is true, so the triangle is a right triangle.
2)
4² + 12² = 13²
16 + 144 = 169
This is false, so the triangle is not a right triangle.
3)
20² + 21² = 27²
400 + 441 = 729
This is false, so the triangle is not a right triangle.
4)
28² + 45² = 53²
784 + 2,025 = 2,809
This is true, so the triangle is a right triangle.