The general equation for a quadratic is y = a*x^{2} + b*x + c, so if you have 3 points, say (-1, 3), (2, 18) and (5, 69), you can use the equations section of the calculator to solve for a, b and c as shown in the images below:

The general equation for a quadratic is y = a*x^{2} + b*x + c, so if you have 3 points, say (-1, 3), (2, 18) and (5, 69), you can use the equations section of the calculator to solve for a, b and c as shown in the images below: