正方形截面立体构造：第二步——构建顶部两条边

① This example demonstrates the second step in constructing a solid with square cross sections, where the top two edges are built after the bottom two edges have been established in the xy-plane, gradually forming the 3D framework. ② The core mathematical concepts involve the method of cross-sections for volume, square cross-sections bounded by function curves, and spatial relationships of edges and faces in solid geometry. ③ Construction highlights: based on the construction summary, GeoGebra commands such as Root, Segment, Point, Polygon, and CurveCartesian are used, with objects including function f, regions R1 and R2, points A and B, and segments a, b, c, d, e, g, to precisely define the top edges. ④ This is suitable for high school or college calculus courses when teaching volume by integration, helping students visualize the step-by-step construction of solids, and can be used for classroom demonstrations or independent student exploration.