Consider the production function Q = aLb where b > 1.Take the first differentiontiation of Q with respect to L. \partial Q/\partial L =ab > 0.Hence the Marginal product of labor is positive .Lets check whether there is diminishing return to labor or not. Again take the second order partial derivative with respect to Labor. \partial ^2Q/\partial L^2 =0.This means that there is constant return to labor. thus, this implies that if the labor increases by 10 units then output also increase by 10 units.