根据余弦定理求出 三点以一点为顶点 形成的夹角

package test;

//根据余弦定理求出 三点以一点为顶点 形成的夹角

public class Jiajiao {

public static void main(String args[]){

java.text.DecimalFormat df = new java.text.DecimalFormat("#0.00");

double x=0;

double y=0;

double x1=2;

double y1=0;

double x2=2;

double y2=2;



double dx1=x1-x;

double dy1=y1-y;

double dx2=x2-x;

double dy2=y2-y;

double c = Math.sqrt(dx1 * dx1 + dy1 * dy1) * Math.sqrt(dx2 * dx2 + dy2 * dy2);

System.out.println("C: "+c);

double angle = Math.acos((dx1 * dx2 + dy1 * dy2) / c);

String temp = df.format(180*angle/Math.PI);

System.out.println(temp);

}

}