《中学生数学》2 0 0 1年 1 1月上期课外练习高二年级第 3题是 :已知直线ｌ :ｘ -ｙ + 6=0 ,圆Ｃ :(ｘ - 3 ) 2+ ( ｙ- 3 ) 2 =4的切线及ｘ轴、ｙ轴围成的四边形有外接圆 ,求此外接圆的方程 .在解答中遗漏了一种情形 :当圆的切线与ｌ平行且与负半ｘ轴、正半 ｙ轴相交时 ,已知四 The mathematics of middle school students in January 1st, 2001, the second year of the second year of extracurricular exercises, the third problem is: the known line l:x -y + 6=0, the circle C: (x - 3 ) 2+ (y - 3 ) The tangent of 2 = 4 and the quadrangle formed by the x and y axes have circumcircles. Find the equation of the circumcircle. In the solution, a case is omitted: When the tangent of the circle is parallel to l and negative x axis, positive When the half y-axis intersects, known four