-x^2+2x-3 is one of many equations that satisfy those conditions.
Any quadratic equation in the form ax^2+bx+c with the following conditions.
b^2-4ac>0. If the descriminate is greater then zero you will have two real solutions or two zeros.
Since you need the end behavior to both point downward. Let a<0 or in other words put any negitive real number for the coefficient of x^2.