说明：  3点画弧，三点绘制圆弧就是已知三点，通过这三点画圆弧。在画圆弧时先选择三点绘制圆弧命令，然后选定圆弧的起点（第一点）、再选定第二点、最后选定终点（第三点），三点绘制圆弧完成。在选择起点、第二点和终点时，可以按顺时针方向选取，也可以按逆时针方向选取。
(3 stipple arc, three three-point arc is drawn is known, an arc through three points. When drawing an arc to three points to draw an arc command, then the arc start point (first point), and then the second point, the final selection of the end point (third point), complete the three-point arc is drawn . When choosing a starting point, the second point and end point, you can a clockwise direction, you can also counterclockwise.)