VB编程急急急!!!

这是个例题，希望对你有所帮助
y=ax^2+bx+c 的形式的一元二次方程,输入a,b,c的值,的到方程的根

Public a As Single
Public b As Single
Public c As Single
Public x1 As Single
Public x2 As Single
Public xs1 As String
Public xs2 As String

Private Sub Command1_Click()
a = Val(Text1.Text)
b = Val(Text2.Text)
c = Val(Text3.Text)
If b * b - 4 * a * c > 0 Then
x1 = (-b + Sqr(b * b - 4 * a * c)) / (2 * a)
x2 = (-b - Sqr(b * b - 4 * a * c)) / (2 * a)
Label4.Caption = "方程有两根，分别为：" & x1 & "," & x2
ElseIf b * b - 4 * a * c = 0 Then
x2 = (-b) / (2 * a)
Label4.Caption = "方程有一根，为：" & x2
Else
xs1 = (-b) / (2 * a) & "+" & Format(Sqr(-(b * b - 4 * a * c)), "0.00") / (2 * a) & "i"
xs2 = (-b) / (2 * a) & "-" & Sqr(-(b * b - 4 * a * c)) / (2 * a) & "i"
Label4.Caption = "方程有两根，分别为：" & xs1 & Chr(13)