The distribution of zeros of solutions for a class of third order differential equation

For third order linear differential equations of the form r(t)x'(t)''+ p(t)x'(t) + q(t)x(t) = 0; we will establish lower bounds for distance between zeros a solution and/or its derivatives. The main results be proved by making use Hardyís inequality, some generalizations Opialís inequality and Boydís inequality.