根据三个点（x1,y1）、（x2,y2）、（x3,y3），确定方程y=aX^2 + bX + c，带入X求得Y

/**

* 给出三个点，根据三个点求解出方程，然后把X带入方程求得Y

* */

public double getYByThreeDotAndX(double a1,double b1,double c1,double d1,double a2,double b2,double c2,double d2,double a3,double b3,double c3,double d3,double X){

*  a1x + b1y + c1z = d1 
*  a2x + b2y + c2z = d2 
*  a3x + b3y + c3z = d3
* 
double x=((d1*c2-d2*c1)*(b2*c3-b3*c2)-(d2*c3-d3*c2)*(b1*c2-b2*c1))/((a1*c2-a2*c1)*(b2*c3-b3*c2)-(a2*c3-a3*c2)*(b1*c2-b2*c1));
double y=((d1*c2-d2*c1)*(a2*c3-a3*c2)-(d2*c3-d3*c2)*(a1*c2-a2*c1))/((a2*c3-a3*c2)*(b1*c2-b2*c1)-(a1*c2-a2*c1)*(b2*c3-b3*c2));
double z=(d1-a1*x-b1*y)/c1;
//x、y、z分别对应Y = aX^2 + bX + c 中的a、b、c
double a = x;
double b = y;
double c = z;

double Y = a * X * X + b * X + c;

return Y;
}