a²-6a+9+√﹙4-b﹚=0
﹙a-3﹚²+√﹙4-b﹚=0
∵ ﹙a-3﹚²≥0,√﹙4-b﹚≥0
又:﹙a-3﹚²+√﹙4-b﹚=0
∴ a-3=0,a=3
4-b=0,b=4
∴ 4-3<c<4+3
1<c<7.