I need help answering a discrete mathematics homework problem. Read the details for the questions. Thanks.?

Prove that if one solution for a quadratic equation of the form x^2 + bx + c = 0 is rational (where b and c are rational), then the other solution is also rational. (Use the fact that if the solutions of the equation are r and s, then x^2 + bx + c = (x - r)(x - s).)