6.15. For each of the following second-order differential equations for causal and sta- ble LTI systems, determine whether the corresponding impulse response is under- damped, overdamped, or critically damped: (a) +4+4y(t)

= x(t) of 201 dr (b) 5+4+5y(t) = 7x(1) dwn di (c) +20 + y(t) = x(1) (d) 5+4 +5y(r) = 7x(r) + Iden