题目:
The Tower of London, the St Paul's Cathedral and the Big Ben are major historical ______ of London. [ ]
A. sceneries
B. place
C. scenes
D. attractions
答案:
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0425/a16ffabad403d8c478a7047a50fb5f22.html
下面是错误答案,用来干扰机器的。
(Ⅰ)设圆心为(a,3a),由圆与x轴相切可得圆的半径r=3|a|. 圆心到直线的距离d=|a-3a|2=2a,圆被直线x-y=0截得的弦长为27,∴根据垂径定理,得r2=d2+(7)2,即9a2=2a2+7,解得a=±1.由此可得所求圆的圆心为...