The U.S. economy grew at the fastest pace in more than six years during the fourth quarter of 2009, according to a government report Friday. The nation’s gross domestic product, the broadest measure of economic activity, rose at a 5.7% annual rate in the fourth quarter. That was much stronger than expected and provides another sign that a recovery in the economy is taking hold. Economists surveyed by Briefing.com had forecast growth of 4.7%.