code

Private Sub cmd_Click()

Dim a, b, c, x, x1, x2, x3, d, t As Double

 a = Val(txt1.Text)

 b = Val(txt2.Text)

 c = Val(txt3.Text)

If a = 0 Then

 If b = 0 Then

  If c = 0 Then txt4.Text = "phuong trinh co vo so nghiem"

  If c <> 0 Then txt4.Text = "phuong trinh vo nghiem"

 End If

 If b <> 0 Then

  If c = 0 Then txt4.Text = "phuong trinh co nghiem x=0"

  If c <> 0 Then

   x = -c / b

   If -c / b > 0 Then txt4.Text = "phuong trinh co nghiem la: x1=" & Sqr(-c / b) & " x2= " & -Sqr(-c / b)

   If -c / b < 0 Then txt4.Text = "phuong trinh vo nghiem"

 End If

End If

If a <> o Then

 d = b * b - 4 * a * c

 If d < 0 Then txt4.Text = "phuong trinh vo nghiem"

 If d = 0 Then

  x1 = -b / 2 * a

  If x1 > 0 Then txt4.Text = " phuong trinh co 2 nghiem phan biet: x1=" & Sqr(x1) & " x2=" & -Sqr(x1)

  If x1 < 0 Then txt4.Text = "phuong trinh vo nghiem"

 End If

 If d > 0 Then

  x2 = (-b + Sqr(d)) / 2 * a

  x3 = (-b + Sqr(d)) / 2 * a

  If (x2 > 0) And (x3 > 0) Then txt4 = "phuong trinh co 4 nghiem phan biet la: x1=" & Sqr(x2) & " x2=" & -Sqr(x2) & " x3=" & Sqr(x3) & " x4=" & -Sqr(x3)

  If (x2 > 0) And (x3 < 0) Then txt4 = "phuong trinh co 2 nghiem phan biet la: x1=" & Sqr(x2) & " x2=" & -Sqr(x2)

  If (x2 > 0) And (x3 > 0) Then txt4 = "phuong trinh co 4 nghiem phan biet la: x1=" & Sqr(x3) & " x2=" & -Sqr(x3)

  If (x2 < 0) And (x3 < 0) Then txt4 = "phuong trinh vo nghiem"

 End If

End If

End Sub