1. For each of the systems represented by the following differential equations, where x(t) and y(t) denote the system's input and output, respectively, determine which ones are linear and which ones are nonlinear by checking both scalability and additivity: (Note: Please check both scalability and additivity, although failure of either one indicates nonlinearity) a) y(t) + 2y(t) = x(t) *b) 3y(t) + y(t) = 2x(t)x(t) c) y(t) + sin(t) y(t) = x(t) + 2x(t)