VB.net2008的功能代码：已知一个平面上的四个点，用最小二乘法求出直线方程。

在VB.NET 2008中，你可以使用Math类的线性代数功能来通过最小二乘法找到通过四个给定点的最佳拟合直线。假设你有四个点的坐标(x1, y1), (x2, y2), (x3, y3), (x4, y4)，可以按照以下步骤编写代码：

Imports System.Math ' 引入数学库

Public Function LeastSquaresFit(points() As Double()) As String ' 函数返回直线方程 Ax + By + C = 0 的形式
    Dim xSum, ySum, xySum, x2Sum As Double
    Dim n As Integer = points.Length - 1 ' 因为最后一维是点的坐标，所以长度减一

    xSum = points(0)(0) + points(1)(0) + points(2)(0) + points(3)(0)
    ySum = points(0)(1) + points(1)(1) + points(2)(1) + points(3)(1)
    xySum = points(0)(0) * points(0)(1) + points(1)(0) * points(1)(1) + points(2)(0) * points(2)(1) + points(3)(0) * points(3)(1)
    x2Sum = points(0)(0)^2 + points(1)(0)^2 + points(2)(0)^2 + points(3)(0)^2

    ' 计算斜率 B 和截距 C
    Dim a = (n * xySum - xSum * ySum) / (n * x2Sum - xSum^2)
    Dim b = (x2Sum * ySum - xySum * xSum) / (n * x2Sum - xSum^2)

    ' 最终方程 A = 1 (因为一般形式是 Ax + By + C = 0，A=1)，然后返回y关于x的线性方程
    Return "y = " & b & "x + (" & a & ")"
End Function

' 示例调用
Dim point1(1) = {1, 2}
Dim point2(1) = {3, 5}
Dim point3(1) = {4, 6}
Dim point4(1) = {6, 9}

Dim lineEquation As String = LeastSquaresFit(New Double()() {point1, point2, point3, point4})
Console.WriteLine(lineEquation)

这段代码会计算通过这四个点的最佳拟合直线，并返回其方程。