使用绘图语句建立一个演示二次函数曲线的窗体程序。其中，三个文本框控件txtA, txtB、txtC用来输入二次函数的参数，图片框Picture1用来显示二次函数曲线，命令按钮cmdXsqx用来启动二次函数曲线的绘画，命令按钮cmdCls用来清除二次函数曲线。-Use the drawing statement establishes a quadratic curve form demonstration program. Among them, three text box controls txtA, txtB, txtC to a quadratic function of the input parameters, Picture1 picture box to display the quadratic curve, the command button to start painting cmdXsqx quadratic curve command button to cmdCls Clear quadratic function curve.