Given a function f(x), its third-order difference quotient can be expressed as f "(x)/x3. Suppose there is a function f(x) and the second derivative f "(x) is known. The goal is to calculate the third-order difference quotient of f(x) at a certain point x0. Mathematically, the third-order difference quotient can be expressed as: third-order difference quotient = f'' (x0)/x0 3. The calculation results are: the third-order difference quotient =0, and the third-order difference quotient of function f(x) at point x0 is 0.