Function RTSEC(X1, X2, XACC:real):real;
Label 99;
var
    MAXIT,J:integer;  FL,F,SWAP,XL,DX,RTS:real;
begin
    MAXIT:=30;
    FL:=FUN(X1);
    F:=FUN(X2);
    If Abs(FL) < Abs(F) Then
    begin
        RTS:=X1;
        XL:=X2;
        SWAP:=FL;
        FL:=F;
        F:=SWAP;
    end
    Else
    begin
        XL:=X1;
        RTS:=X2;
    end;
    For J:=1 To MAXIT do
    begin
        DX:=(XL - RTS) * F / (F - FL);
        XL:=RTS;
        FL:=F;
        RTS:=RTS + DX;
        F:=FUN(RTS);
        If (Abs(DX) < XACC) Or (F = 0) Then goto 99;
    end;
    ShowMessage('RTSEC exceed maximum iterations');
99: RTSEC:=RTS;
end;