string(264) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E4%B8%80%E5%85%83%E4%BA%8C%E6%AC%A1%E6%96%B9%E7%A8%8B%E7%9A%84%E8%A7%A3%E5%85%AC%E5%BC%8F%E6%B3%95 => Failed to connect to 14.18.46.51 port 38206: Connection refused"
一元二次方程的解公式法
