Divide through by p



The sum of the roots is the coefficient of x with the opposite sign, -3q/p.
Since the roots are equal, let them be r and r.




The product of the roots is the constant term 9/p.
Since the roots are both r, their product is r2.



So we have a system of equations to solve



Solve the first for r



Substitute in the 2nd equation in the system:





Cross-multiply:





p cannot be 0, so we may divide both sides by it



Edwin