Function RTFLSP(X1, X2, XACC:real):real;
Label 99;
var
    XL,XH,SWAP,FL,FH,RTF,DX,F,DEL:real;  J,MAXIT:integer;
begin
    MAXIT:=30;
    FL:=FUN(X1);
    FH:=FUN(X2);
    If FL * FH > 0 Then
        ShowMessage('Root must be bracketed for false position');
    If FL < 0 Then
    begin
        XL:=X1;
        XH:=X2;
    end
    Else
    begin
        XL:=X2;
        XH:=X1;
        SWAP:=FL;
        FL:=FH;
        FH:=SWAP;
    end;
    DX:=XH - XL;
    For J:=1 To MAXIT do
    begin
        RTF:=XL + DX * FL / (FL - FH);
        F:=FUN(RTF);
        If F < 0 Then
        begin
            DEL:=XL - RTF;
            XL:=RTF;
            FL:=F;
        end
        Else
        begin
            DEL:=XH - RTF;
            XH:=RTF;
            FH:=F;
        end;
        DX:=XH - XL;
        If (Abs(DEL) < XACC) Or (F = 0) Then goto 99;
    end; 
    ShowMessage('RTFLSP exceed maximum iterations');
99: RTFLSP:=RTF;
end;