How do you compute quadratic equation using java?

Answer 1

What do you mean by "compute"? Do you want to graph it? Factor it? Calculate it's function given a set of points that lie on it?

If you're looking to compute the function given three points that fall on the parabola, then I have just the code for you. If you're given three points, (x1, y1), (x2, y2) and (x3, y3), then you can compute the coefficients of your quadratic equation like this:

a = (y1 * (x2 - x3) + y2 * (x3 - x1) + y3 * (x1 - x2)) / (x1 * x1 * (x2 - x3) + x2 * x2 * (x3 - x1) + x3 * x3 * (x1 - x2))

b = (y1 - y2) / (x1 - x2) - a * (x1 + x2);

c = y1 - (x1 * x1) * a - x1 * b;

You now can calculate the y co-ordinate of any point given it's x co-ordinate by saying:

y = a * x * x + b * x + c;