题目

For more than twenty years scientists have been searching for signs of life on other planets. Most of these searches have been done over the radio. The hope is that someone in outer space may be trying to get in touch with us. Scientists also have sent radio and television messages on spaceships traveling through space, on the chance that someone may be receptive （善于接受的） to such messages. Scientists are using powerful radio telescope to listen to signals from about 1,000 stars, all within 100 light years of earth. In addition, they will scan (扫视) the entire sky to “（2005•广州）若a2-2a+1=0，则2a2-4a=    ．