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个根-Create a sub-vi find the root of the quadratic equation x constants a, b, and c are real numbers. From 3 of front panel control terminal, used to input a, b, c　two indicators showing two root