Построение графика функции по заданному параметрическому представлению - VB

Option Explicit
 
Private Sub Form_Load()
    Dim t As Single, a As Single, x As Single, y As Single
    AutoRedraw = True: Scale (-10, 20)-(35, -20): a = 15
    For t = 0 To 6.28318530717959 Step 0.01
        x = a * Cos(t) * (1 + Cos(t)): y = a * Sin(t) * (1 + Cos(t))
        If t = 0 Then PSet (x, y) Else Line -(x, y)
    Next
End Sub