2 Let convex quadrilateral $A B C D$ satisfy $A B=A D=1, \angle A=160^{\circ}, \angle C=$ $100^{\circ}$, then the range of the length of diagonal $A C$ is $\qquad$ .
(2) $\{1\}$ Hint: Since $\angle C=180^{\circ}-\frac{\angle A}{2}$, points $B$, $C$, and $D$ lie on a circle with center $A$ and radius 1.