解答这道题---**Textual Information:** * **Question Stem:** 如图, 图1是长方形纸带, 将纸带沿EF折叠成图2, 再沿BF折叠成图3, 若图3中∠CFE = x°, 则图1中的∠DEF的度数用x的代数式表示是____. * **Other Relevant Text:** 图 1, 图 2, 图 3. Handwritten annotations: α (near ∠AEF in 图1 and 图2), 180-α (below 图1 and 图2, and near ∠EFB in 图1 and ∠BFG in 图3), 180-α-α (near top right and below 图3). **Chart/Diagram Description:** * **Type:** Sequence of three geometric diagrams illustrating paper folding. * **Main Elements:** * **Diagram 1 (图1):** A rectangle ABCD. Points E on AD, F on BC. Line segment EF drawn. Handwritten label 'α' near angle AEF. Right angle symbol near angle BFE. Handwritten text '180-α' below the diagram. * **Diagram 2 (图2):** Result of folding 图1 along EF. Part ABEF is folded to GBEF. Point G is the image of A. Line segment EG is formed. Handwritten label 'α' near angle GEF and angle AEF. Angle BFE is shown. Angles EFG and BFG are marked with red arcs. Handwritten text '180-α' below the diagram. An arrow indicates transformation from 图1 to 图2. * **Diagram 3 (图3):** Result of folding 图2 along BF. Part EFG is folded to IFG. Point I is the image of E. Line segment FI is formed. Angles EFG and IFG are marked with red arcs (equal). Angle BFG is also marked with a red arc. Angle CFE is marked with a blue arc and labeled 'x°'. Handwritten text '180-α-α' near the top right and below the diagram. Green lines indicate the folded position of the edge CD. An arrow indicates transformation from 图2 to 图3.