27. 已知圆C1:x2+y2−2x−2y+1=0C_{1}:x^{2}+y^{2}-2x-2y+1=0C1:x2+y2−2x−2y+1=0,圆C2:(x−4)2+(y−5)2=r2(r>0)C_{2}:(x-4)^{2}+(y-5)^{2}=r^{2}(r>0)C2:(x−4)2+(y−5)2=r2(r>0).(1)若圆C1C_{1}C1与圆C2C_{2}C2外切,求rrr的值;(2)若圆C1C_{1}C1与圆C2C_{2}C2有两个交点,求rrr的取值范围.