Chef and his love

Chef is in love with his girlfriend chefina.Now,after being in relationship for so many years chef tries to propose chefina for marriage. Chefina being a mathematics lover ,gives a equation of many-one function to chef and put a condition that she will marry him only when he will be able to find the roots of the given function in a given range. $f(x)=(x-k_{1})*(x-k_{2})*(x-k_{3})*(x-k_{4})