这道题怎么做---**Textual Information:** **Question Stem:** 7. 如图, 正方形 ABCD 的边长为 4, E 为 AB 的中点, 将△ADE 沿直线 DE 折叠后, 点 A 落在点 F 处, DF 交对角线 AC 于 G, 则 FG 的长是______. **Translation (for clarity, not part of required output):** 7. As shown in the figure, square ABCD has side length 4, E is the midpoint of AB. After folding △ADE along the line DE, point A falls on point F, DF intersects diagonal AC at G, then the length of FG is______. **Other Relevant Text:** Side length of square ABCD is 4. E is the midpoint of AB. Triangle ADE is folded along DE. Point A falls on point F. DF intersects diagonal AC at G. Find the length of FG. **Diagram Labels:** Points: A, B, C, D, E, F, G Lines: Square sides AB, BC, CD, DA. Diagonal AC. Line segments DE, DF, EG, DG, FG. **Chart/Diagram Description:** * **Type:** Geometric figure, specifically a square with internal lines and points. * **Main Elements:** * **Shape:** A square labeled ABCD. * **Points:** Vertices of the square are A (bottom left), B (bottom right), C (top right), D (top left). Point E is on the bottom side AB, located at the midpoint. Point F is located inside the square to the right of the center. Point G is located inside the square, on the diagonal AC and the line segment DF. * **Lines:** The sides of the square AB, BC, CD, DA. A diagonal AC connects A and C. A line segment DE connects D and E. A line segment DF connects D and F. Line segment EF connects E and F. Line segment DG connects D and G. Line segment AG connects A and G. Line segment CG connects C and G. * **Relationships:** E is the midpoint of AB. The figure shows that triangle ADE is folded along DE to obtain triangle FDE, so triangle ADE is congruent to triangle FDE. Point F is the image of point A after the fold. Line segment DF is the image of line segment DA after the fold. Line segment EF is the image of line segment AE after the fold. Diagonal AC intersects DF at point G. * **Given Information from Text (reflected in diagram):** ABCD is a square with side length 4. E is the midpoint of AB. Folding △ADE along DE maps A to F. DF intersects AC at G.