题目内容

过三点A(1，1，一1)，B(-2，一2，2)和C(1，一1，2)的平面方程是______．

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设平面方程为Ax+Cz+D=0，其中A，C，D均不为零，则平面 ( )

A. 平行于x轴
B. 平行于y轴
C. 经过x轴
D. 经过y轴

已知曲面z=x2+y2上点P处的切平面平行于平面2x+2y+z一1=0，则点P的坐标是 ( )

A. (1，一1，2)
B. (一1，1，2)
C. (1，1，2)
D. (一1，一1，2)

You have received a letter from Sophia. She expressed her admiration for micro-blogging and wondered whether it can replace books as the main learning resources. Write a reply letter to explain your opinions. You should write about 100 words on the ANSWER SHEET. Do not sign your own name at the end of the letter. Use "Li Ming" instead. Do not write the address. (10 points)

曲线x2+y2+z2=a2与x2+y2=2ax(a>0)的交线是 ( )

A. 抛物线
B. 双曲线
C. 圆
D. 椭圆