Which best explains why this triangle is or is not a right triangle? A triangle with side lengths 36 inches, 15 inches, 39 inches. This triangle is not a right triangle: 39 squared + 15 squared not-equals 36 squared. This triangle is not a right triangle: 39 squared + 36 squared not-equals 15 squared. This triangle is a right triangle: 36 squared + 39 squared = 15 squared. This triangle is a right triangle: 36 squared + 15 squared = 39 squared.