[NumLock]

если совсем лень самому писать, то:
(WebBrowser.Document as IHTMLDocument2).parentWindow.execScript('var r='+Edit.Text+'; document.write(r+"<br>");', 'javascript');

список математических функций: http://www.spravkaweb.ru/jscript/objects/math/

Код:

unit Unit1;

interface

uses
  MSHTML,
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  StdCtrls, ExtCtrls, OleCtrls, SHDocVw;

type
  TFormMain = class(TForm)
    WebBrowser: TWebBrowser;
    Panel: TPanel;
    Edit: TEdit;
    Button: TButton;
    Memo: TMemo;
    procedure FormCreate(Sender: TObject);
    procedure ButtonClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  FormMain: TFormMain;

implementation

{$R *.dfm}

procedure TFormMain.FormCreate(Sender: TObject);
begin
  if WebBrowser.Document=nil then WebBrowser.Navigate('about:blank');
  while WebBrowser.Document=nil do Application.ProcessMessages;
end;

procedure TFormMain.ButtonClick(Sender: TObject);
begin
  (WebBrowser.Document as IHTMLDocument2).body.innerText:='';
  (WebBrowser.Document as IHTMLDocument2).parentWindow.execScript('var r='+Edit.Text+'; document.write(r+"<br>");', 'javascript');
  Memo.Lines.Insert(0, (WebBrowser.Document as IHTMLDocument2).body.innerText);
end;

end.

http://data.cod.ru/84745