Answer
(a) $e^{-2x}$ is a solution.
(b) $x e^{-2x}$ is not a solution.
(c) $x^2 e^{-x}$ is not a solution.
(d) $2x e^{-2x}$ is not a solution.
Work Step by Step
(a) $e^{-2x}$ is a solution.
(b) $x e^{-2x}$ is not a solution.
(c) $x^2 e^{-x}$ is not a solution.
(d) $2x e^{-2x}$ is not a solution.
