x^2+y^2-2(t+3)x+2(1-4t^2)y+16t^4+9=0
(x-t-3)^2+(y+1-4t^2)^2+7t^2-6t=0
(x-t-3)^2+(y+1-4t^2)^2=6t-7t^2
6t-7t^2＞0 得：0＜t＜6/7
所以：t取值范围0＜t＜6/7