Question

g'vn the following 3 ordinary differential eqns, where x is the dependent variable and t is the independent variable. which is linear? (a) 2 (d^2*x/dt^2) + 2x dx/dt=0
(b) 2 (d^2x/dt^2)+2xdx/dt+t^2=e^-t
(c) 2(d^2x/dt^2)+2t(dx/dt)=0