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Prompt
A course app that helps adults relearn mathematics through hands-on interaction (390×844), with an English interface: a course map and lessons composed of small interactive steps, each requiring an action rather than reading an explanation.
The core is a lesson explaining why a circle's area is πr²: cut the circle into sectors, drag a slider to make the slices finer and arrange them alternately, and assemble a near-rectangle whose sides are πr and r. Let the formula emerge from the geometry. Follow it with a short question, with specific feedback for both correct and incorrect answers.
Design three screens: the course map; the circle halfway through unfolding into a rectangle; and answering a question with feedback. Deliver `index.html` and `screens.html` with the three screens side by side.
View Chinese original
一个让成年人通过动手重新学数学的课程 App（390×844），界面用英文：课程地图，以及由一小步一小步互动组成的课，每一步都要求用户动手操作，而不是读一段讲解。
核心是一节讲“圆的面积为什么是 πr²”的课：把圆切成扇形，拖动滑杆切得越来越细并交错铺开，扇形拼成一个近似长方形，两条边分别是 πr 和 r，公式从图形里自己长出来。之后有一道小题，答对、答错各有具体的反馈。
设计三屏：课程地图、拖动到一半的圆变长方形、答题与反馈。交付 `index.html` 和三屏并排的 `screens.html`。
