getSymmetric(v) {
    const tha2 = v.getGradient();
    const tha1 = this.getGradient();
    const tha = 2 * (tha1 - tha2);

    const oldx = v.x;
    const oldy = v.y;

    v.x = oldx * Math.cos(tha) - oldy * Math.sin(tha);
    v.y = oldx * Math.sin(tha) + oldy * Math.cos(tha);

    return v;
  }
Calculates the symmetric vector of a given vector with respect to the line.
@param {Vector2D} v - The vector to reflect.
@returns {Vector2D} The reflected vector.