General Electric said today that its health care unit would buy IDX Systems Corp., which produces software for hospitals and doctors’ offices, in a deal the companies valued at US$1.2 billion. Shareholders of South Burlington, Vt.-based IDX are to get $44 a share in cash, representing a 25 percent premium over the stock’s closing price yesterday. IDX shares soared $8.03, or 23 percent, to $43.20 in early trading on the Nasdaq Stock Market, while shares of GE fell 23 cents to $33.26 on the New York Stock Exchange.