请解读第一题并给出详细思路过程---**Question 1**
**Question Stem:**
1. 如图,在矩形纸片 ABCD 中,点 E 在 BC 边上,将 △CDE 沿 DE 翻折得到 △FDE,点 F 落在 AE 上.若 CE = 3 cm,AF = 2EF,则 AB = \_\_\_\_\_\_ cm.
**Translation of Question Stem:**
1. As shown in the figure, in rectangular paper ABCD, point E is on side BC. Fold △CDE along DE to get △FDE, where point F falls on AE. If CE = 3 cm and AF = 2EF, then AB = \_\_\_\_\_\_ cm.
**Given Information:**
* Figure shows a rectangle ABCD.
* Point E is on BC.
* △CDE is folded along DE to get △FDE.
* Point F lies on AE.
* CE = 3 cm.
* AF = 2EF.
**To Find:**
AB
**Provided Answer (Underline indicates fill-in-the-blank):**
3√5
**Diagram Description:**
* **Type:** Geometric figure illustrating a rectangle and folding.
* **Main Elements:**
* A rectangle ABCD with vertices labeled A, B, C, D in counterclockwise order.
* Point E is on the side BC.
* Line segments AE, DE, and DF are drawn.
* Triangle CDE is shown, shaded in gray.
* Point F is located on the line segment AE.
* Dashed line segment CD is implied as the original position of DF after folding.
* The figure is labeled "第 1 题图" (Figure for Question 1).