form1.frm

蒋加伏主编VB程序设计第四版PPT及全部课本源码 北京邮电大学出版社 Visual Basic 程序设计教程（第四版） 主编 蒋加伏 张林峰 找了好久的（不带密码的）

VERSION 5.00
Begin VB.Form Form1 
   Caption         =   "例[5-19] 求方程的根"
   ClientHeight    =   3195
   ClientLeft      =   60
   ClientTop       =   345
   ClientWidth     =   4680
   LinkTopic       =   "Form1"
   ScaleHeight     =   3195
   ScaleWidth      =   4680
   StartUpPosition =   3  '窗口缺省
End
Attribute VB_Name = "Form1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Private Sub Form_Click()
'采用Newton迭代法 , 迭代公式: Xn 1 = Xn - f(Xn) / f '(Xn)
'本题f(x) = x ^ 3 - 2 * x - 5
Dim x As Single, x1 As Single
Dim f As Single, f1 As Single
x = 1.5                             'x任取[1.5，2.5]中的一个值
Do
x1 = x
f = x ^ 3 - 2 * x - 5
f1 = 3 * x ^ 2 - 2
x = x1 - f / f1
Loop Until (Abs(x - x1) < 0.00001)
x = Fix(x * 100 + 0.5) / 100      '四舍五入精确到小数点后第二位
Print "方程X^3-2X-5=0在区间[1.5,2.5]上的一个实根是："; x
End Sub