Private Sub CommandButton1_Click()
Dim a, b, c, d  As Integer
Dim x1, x2 As Double
a = val(InputBox1("Введите параметр a"))
b = val(InputBox2("Введите параметр b"))
c = val(InputBox3("Введите параметр c"))
d = (b ^ 2) - (4 * a * c)
 MsgBox("d=" & d)
 Select Case d
 Case Is < 0
  MsgBox("НЕТ РЕШЕНИЯ")
  Case 0
  x1 = (-b) / (2 * a)
  x2 = (-b) / (2 * a)
 TextBox5 = "x1=" & x1 & "x2=" & x2
 Case Is > 0
 x1 = (-b + Sqr(d)) / (2 * a)
  x2 = (-b - Sqr(d)) / (2 * a)
 MsgBox("x1=" & x1 & "x2=" & x2)
 End Select

End Sub