Which describes the concavity of the function f(x)=(x^2-1)/e^x, -2.5

The domain of the following relation: r: {(3, 5), (8, 6), (2, 1), (8, 6)} is (1 point) no domain exists {1, 5, 6} {3, 8, 2, 8} {2, 3, 8}