For which values of r is y=ert a solution to the differential equation y\'\'\'+y\'\'-4y\'-4y=0? Solution y\'\'\'+y\'\'-4y\'-4y=0? taking characterstic equation s^3 + s^2 -4s -4 = 0 solving we will get s={-2, -1, 2} thus r values are -2 , -1 ,2 y=ert a solution to the differential equation.