给你介绍个网址：http://zhidao.baidu.com/link?url=WdmK8lW-VlMqTtvkBxig65DyC6CqA1NEZ4_NcbOWuQimphHfr1BUbKLM3HmxNp2PGvyorOKHH8fVHXngrbXP56aXwToAUBBGiAZpSoN6JjK2x-y+2z=8(1)y+2z=-2(2)3x+y-4z=1(3)(1)+(2)2x+...