Option Explicit

Private Sub cmdCalc_Click()

Dim a As Single, b As Single, c As Single

Dim delta As Single, preal As Single, pimg As Single

a = Val(txtA.Text)

b = Val(txtB.Text)

c = Val(txtC.Text)

If a = 0 Then

MsgBox "A equação tem que ser de grau 2!"

Exit Sub

End If

delta = b * b - 4 * a * c

If delta >= 0 Then

txtR1 = (-b + Sqr(delta)) / 2 / a

txtR2 = (-b - Sqr(delta)) / 2 / a

Else

preal = -b / 2 / a

pimg = Sqr(-delta) / 2 / a

txtR1 = preal & " + i" & pimg

txtR2 = preal & " - i" & pimg

End If

End Sub