Well I am asked to do this : (VBA EXCEL) Write a user-defined vba function to de

Question

Well I am asked to do this : (VBA EXCEL)

Write a user-defined vba function to determine the real root of f(x) = 5x^3 - 5x^2 + 6x - 2 when xl = 0 xu = 1 and es = 1%.

Below is my code, and I do not know why it is not working or what is wrong with it. It does not work. Please help!!

Function f(x) f=5*x^3-5*x^2+6*x-2 End Function Function Bisect(xl, xu, es) Performs Bisection method Dim xrold As Double, test As Double su=1 tsl = f(xl ) ea-100 Relative Error to test xtold =su 'Initial guess of the root loops 0 'Will be used for counting Do While ea eAnd loops 50 XC = (x1 +xy) / 2 loops loops +1 If O Then End If test-f(xl) * f(&W; If test 0 Then Else End If lfea= 50 Then Exit Do Loop Bisectx Sheets("Q3" Cells(4, 7) End Function

Explanation / Answer

Module VBModule

Function Fun(ByVal x As Double)
return (5 * (x ^ 3)) - (5 * (x ^ 2)) + (6 * x) - 2
End Function

Sub Bisect(ByVal xl As Double, ByVal xu As Double, ByVal es As Double)
Dim itr As Integer
Dim xr As Double, xrOld As Double, err As Double, test As Double, newErr As Double
itr = 0
xr = xl
es = es / 100.0
  
Do while True
xrOld = xr
xr = (xl + xu) / 2.0
itr = itr + 1
  
test = Fun(xl) * Fun(xr)
  
newErr = Math.Abs((xr - xrold) / xr) * 100
  
If test < 0 Then
xu = xr
ElseIf test > 0 Then
xl = xr
Else
newErr = 0
End If
  
If newErr <= es Then
Exit Do
End If
Loop
Console.WriteLine(xr)
End Sub

Sub Main()
Bisect(0, 1, 1)
End Sub
  
End Module

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