class Point {    private x: number;    private y: number;    constructor(x: number, y: number) {      this.x = x;      this.y = y;    }    public distance(otherPoint: Point): number {      return Math.sqrt(          Math.pow(this.x - otherPoint.getX(), 2) +          Math.pow(this.y - otherPoint.getY(), 2));    }    public getX() {      return this.x;    }    public getY() {      return this.y;    }  }  class Circle {    private center: Point;    private radius: number;    constructor(center: Point, radius: number) {      this.radius = radius;      this.center = center;    }    public isInside(otherPoint: Point): boolean {      return this.center.distance(otherPoint) < this.radius;    }  }  class Triangle extends Point {      private z: number;      constructor(x:number, y: number, z: number){          super(x, y);          this.z = z;      }    public getZ(){        return this.z    }    public getPerimeter (otherPoint: Triangle): number{        return otherPoint.getX() + otherPoint.getY() + otherPoint.getZ()    }  }  let per = new Triangle(24, 61, 32);  console.log(per);所以當我嘗試編譯時它說private x: number;            ^SyntaxError: Unexpected identifier