49. As shown in the figure, in rectangle $A B C D$, with point $B$ as the center and the length of $B C$ as the radius, draw an arc intersecting side $A D$ at point $E$. Connect $B E$, and draw $C F \perp B E$, with the foot of the perpendicular at $F$. Then, the line segment in the figure that has the same length as $B F$ is . $\qquad$
Answer: $A E$