Dim xx() As Single Dim yy() As Single Dim i As Integer Dim s1 As Single Dim s2 As Single Dim s3 As Single Dim s4 As Single Dim al, bl, cl, dl, el, fl As Single Dim ar, br, cr, dr, er, fr As Single Dim wl As Single Dim wr As Single Dim k As Single Private Sub Form_Load() Form1.Scale (-100, -100)-(100, 100) Form1.Line (-100, 0)-(100, 0), vbRed Form1.Line (0, -100)-(0, 100), vbRed End Sub Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) i = i + 1 ReDim Preserve xx(1 To i) ReDim Preserve yy(1 To i) xx(i) = X yy(i) = Y 1 

Form1.Circle (X, Y), 2, vbBlue End Sub Private Sub 画抛物线_Click() s1 = 0 s2 = s1 + Sqr((xx(1) - xx(2)) ^ 2 + (yy(1) - yy(2)) ^ 2) s3 = s2 + Sqr((xx(2) - xx(3)) ^ 2 + (yy(2) - yy(3)) ^ 2) s4 = s3 + Sqr((xx(3) - xx(4)) ^ 2 + (yy(3) - yy(4)) ^ 2) cl = ((s3 - s1) * (xx(2) - xx(1)) - (s2 - s1) * (xx(3) - xx(1))) / ((s3 - s1) * (s2 ^ 2 - s1 ^ 2) - (s2 - s1) * (s3 ^ 2 - s1 ^ 2)) bl = ((xx(2) - xx(1) - cl * (s2 ^ 2 - s1 ^ 2))) / (s2 - s1) al = xx(1) - bl * s1 - cl * s1 ^ 2 fl = ((s3 - s1) * (yy(2) - yy(1)) - (s2 - s1) * (yy(3) - yy(1))) / ((s3 - s1) * (s2 ^ 2 - s1 ^ 2) - (s2 - s1) * (s3 ^ 2 - s1 ^ 2)) el = ((yy(2) - yy(1) - fl * (s2 ^ 2 - s1 ^ 2))) / (s2 - s1) dl = yy(1) - el * s1 - fl * s1 ^ 2 cr = ((s4 - s2) * (xx(3) - xx(2)) - (s3 - s2) * (xx(4) - xx(2))) / ((s4 - s2) * (s3 ^ 2 - s2 ^ 2) - (s3 - s2) * (s4 ^ 2 - s2 ^ 2)) br = ((xx(3) - xx(2) - cr * (s3 ^ 2 - s2 ^ 2))) / (s3 - s2) ar = xx(2) - br * s2 - cr * s2 ^ 2 fr = ((s4 - s2) * (yy(3) - yy(2)) - (s3 - s2) * (yy(4) - yy(2))) / ((s4 - s2) * (s3 ^ 2 - s2 ^ 2) - (s3 - s2) * (s4 ^ 2 - s2 ^ 2)) er = ((yy(3) - yy(2) - fr * (s3 ^ 2 - s2 ^ 2))) / (s3 - s2) dr = yy(2) - er * s2 - fr * s2 ^ 2 For s = s1 To s3 X1 = al + bl * s + cl * s ^ 2 Y1 = dl + el * s + fl * s ^ 2 Form1.PSet (X1, Y1), vbRed Next For s = s2 To s4 X1 = ar + br * s + cr * s ^ 2 Y1 = dr + er * s + fr * s ^ 2 Form1.PSet (X1, Y1), vbRed Next End Sub Private Sub 曲线拟合_Click() For s = s2 To s3 X = ((1 - (s - s2) / (s3 - s2)) ^ 2 * (1 + 2 * (s - s2) / (s3 - s2))) * (al + bl * s + cl * s ^ 2) + (((s - s2) / (s3 - s2)) ^ 2 * (3 - 2 * (s - s2) / (s3 - s2))) * (ar + br * s + cr * s ^ 2) Y = ((1 - (s - s2) / (s3 - s2)) ^ 2 * (1 + 2 * (s - s2) / (s3 - s2))) * (dl + el * s + fl * s ^ 2) + (((s - s2) / (s3 - s2)) ^ 2 * (3 - 2 * (s - s2) / (s3 - s2))) * (dr + er * s + fr * s ^ 2) Form1.PSet (X, Y), vbRed Next End Sub 2