创建子vi求出一元二次方程的根x，这里常量a,b和c是实数。前面板共有3个控制端，用来输入a,b,c 两个指示器显示2个。(Create the child VI and find the root X of the unary two equation, where constants a, B, and C are real numbers. The front panel has 3 control points for inputting a, B, C, and two indicat