题目

过点A(1，－1)，B(－1,1)且圆心在直线x＋y－2＝0上的圆的方程是________． 答案：解析：易求得AB的中点为(0,0)，斜率为－1，从而其垂直平分线为直线y＝x，根据圆的几何性质，这条直线应该过圆心，将它与直线x＋y－2＝0联立得到圆心O(1,1)，半径r＝|OA|＝2. 答案：(x－1)2＋(y－1)2＝4________ in every aspect of his company's business, Paul made himself busy day and night. [      ]A. Being involved  B. InvolvedC. Involving  D. To involve