从三角形顶点访问区域

Question

我正在尝试编写Java代码，该代码获取三角形的顶点（这将是用户输入）并输出所述三角形的面积。我得到NaN作为回应。我应该把我的类型改成float吗？我是不是要走更长的路来解决这个问题？

使用的公式有Distance公式和Heron公式。

import java.util.Scanner;
public class TriangleArea {
    public static void main(String[]args){
        Scanner user = new Scanner(System.in);
        System.out.println("To compute the area of a triangle, please input a point in a vertex when prompted");
        System.out.println("Please input X of the first vertex: x ");
        double firstVertexX = user.nextDouble();
        System.out.println("Please input Y of the first vertex: y ");
        double firstVertexY = user.nextDouble();        
        System.out.println("Please input X  of the second vertex: x");
        double secondVertexX = user.nextDouble();
        System.out.println("Please input Y of the second vertex: y ");
        double secondVertexY = user.nextDouble();       
        System.out.println("Please input X of the third vertex: x");
        double thirdVertexX = user.nextDouble();
        System.out.println("Please input Y of the third vertex: y");
        double thirdVertexY = user.nextDouble();        
        double sideOneX = Math.pow(firstVertexX * 1, 2) - Math.pow(secondVertexX * 2, 2);
        double sideOneY = Math.pow(firstVertexY * 1, 2) - Math.pow(secondVertexY * 2, 2);
        double sideOne = Math.pow(sideOneX + sideOneY, .5);
        double sideTwoX = Math.pow(secondVertexX * 1, 2) - Math.pow(thirdVertexX * 2, 2);
        double sideTwoY = Math.pow(secondVertexY * 1, 2) - Math.pow(thirdVertexY * 2, 2);
        double sideTwo = Math.pow(sideTwoX + sideTwoY, .5);
        double sideThreeX = Math.pow(thirdVertexX * 1, 2) - Math.pow(firstVertexX * 2, 2);
        double sideThreeY = Math.pow(thirdVertexY * 1, 2) - Math.pow(firstVertexY * 2, 2);
        double sideThree = Math.pow(sideThreeX + sideThreeY, .5);
        double s = (sideOne + sideTwo + sideThree)/2;
        double areaStepOne = (s - sideOne) * (s - sideTwo) * (s - sideThree);
        double areaStepTwo = s * areaStepOne;
        double area = Math.pow(areaStepTwo, .5);
        System.out.println("The area of the triangle is " + area + ".");
        System.out.println("The area of the triangle is " + area);
    }
}

Answer 1

问题是计算错误。

从（x1，y1）到（x2，y2）的线段长度为sqrt（（x1-x2）^2+（y1-y2）^2）。

你计算的是：sqrt（x1^2-（x2*2）^2+y1^2-（y2*2）^ 2）。这可能是负面的，给你NaN。

我会把线路改成：

double sideOneX = firstVertexX - secondVertexX;
double sideOneY = firstVertexY - secondVertexY;
double sideOne = Math.sqrt(sideOneX * sideOneX + sideOneY * sideOneY);

（您可以只使用Math.sqrt(v)而不是Math.pow(v, .5)。）

Answer 2

我建议您使用更简单的分析公式

|(X2 - X0) (Y1 - Y0) - (X1 - X0) (Y2 - Y0)| / 2

不取绝对值，符号告诉你三角形是顺时针还是逆时针。