已知圆C的方程为(x-1)2+(y-2)2=4,则圆C的圆心坐标和半径r分别为 发布时间:2017-04-22 14:28 │ 来源:www.tikuol.com 题型:选择题 问题: 已知圆C的方程为(x-1)2+(y-2)2=4,则圆C的圆心坐标和半径r分别为 [ ]A.(1,2),r=2 B.(-1,-2),r=2 C.(1,2),r=4 D.(-1,-2),r=4
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题型:选择题 设U为所有属性,X、Y、Z为属性集,Z=U-X-Y。下列关于函数依赖和多值依赖的叙述中,哪些是正确的( ) Ⅰ.若X→Y,则X→→Y Ⅱ.若X→→Y,则X→Y Ⅲ.若X→Y,则X→Z Ⅳ.若X→→Y,则X→→Z Ⅴ.若X→→Y,则X→→Y'A.仅Ⅰ、Ⅱ和Ⅲ B.仅Ⅱ、Ⅲ和ⅤC.仅Ⅰ和Ⅳ D.仅Ⅳ和Ⅴ 查看答案