求解哈，请问这一句哪错了。

Question

import java.io.*;import java.math.*;public class xianduan extends jisuan{public static void main(String args[]){try{BufferedReader br=new BufferedReader(new InputStreamReader(System.in));System.out.println("输入X1");x1=Integer.parseInt(br.readLine());System.out.println("输入Y1");y1=Integer.parseInt(br.readLine());System.out.println("输入X2");x2=Integer.parseInt(br.readLine());System.out.println("输入Y2");y2=Integer.parseInt(br.readLine());}catch(IOException e){}jisuan L=new jisuan(x1,x2,y1,y2);L.cs();}}class jisuan{static int x1,x2,y1,y2;public jisuan(){}jisuan(int x1,int x2, int y1,int y2){this.x1=x1;this.x2=x2;this.y1=y1;this.y2=y2;}public void cs(){double length;length=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));System.out.println("线段长度为 "+length);}}length=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));

Answer 1

Math.sqrt