1圆C过点P(1,1)且与圆M:(x+2)^2+(y+2)^2=r^2(r>0)关于直线x+y+2=0对称,则点P(1,1)关于直线x+y+2=0对称的点P'(-3,-3)在圆M上.将P'(-3,-3)坐标代入圆M得:1+1=r^2;则r=√2.而圆M的圆心(-2,-2)到直线x+y+2=0的距离d=|-2-2+2|/√2=√2=r,则说明圆M与直线x+y+2=0相切;由于圆C与圆M关于直线x+y+2=0对称,则圆C与直线x+y+2=0相切;且切于同一点.由此可知,圆C与圆M相切于点(-1,-1).21)设PA=a;PB=b;PA和直线PB 互相垂直,即∠APB=90°,则AB一定是⊙C的直径.则a^2+b^...
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