string(266) "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%E6%B3%95%E5%85%AC%E5%BC%8F%E8%BF%87%E7%A8%8B => Received HTTP code 403 from proxy after CONNECT"
一元二次方程的解法公式过程
