### Linearity, order, casuality, and time variance for systems

What are the linearity, order, causality, and time variance of each input-output relationship for systems? 1. (dy/dt) + (1/RC)y(t) = x(t) when RC = constant 2. (dy/dt) + (t^2)y(t) = x(t) 3. (d^2y/dt^2) + y(t)(dy/dt) + y(t) = x(t) 4. y(t) = x^2(t) + 1