如图所示,一张平行四边形纸片 PQRS 沿着两条虚线 TS 和 UR 折叠,如图 1 所示。在图 2 中, 且 。

- (a)
求图 2 中的 。
- (b)
求图 2 中的 。
它不会直接告诉你答案,而是问你卡在哪一步看看 AI 是怎么陪你一步步弄懂这道题的
完整解法
10(a)
1. Relate the folded angle $\angle UQR$ to the original angle of the parallelogram.
When the paper is folded, the angle in Figure 2 corresponds directly to the original interior angle of the parallelogram PQRS before folding because the shape around Q is preserved under folding.
Since PQRS is a parallelogram, the opposite interior angles are equal:
2. Calculate the original interior angle $\angle PSR$ to find $\angle UQR$.
The fold line is perpendicular to the parallel horizontal sides and of the parallelogram. Therefore, the angle between the vertical line and the base is (i.e., ).
The full angle at before folding, , is the sum of the angle of the folded part and the right angle:
Thus,
10(b)
1. Find the interior angles of the original parallelogram PQRS.
In the original parallelogram , we are given in the folding diagram that after folding along the vertical line , the remaining angle is .
Since , in the unfolded state, the angle at of the right-angled triangle is .
Therefore, the original angle of the parallelogram is:
Since adjacent angles in a parallelogram sum to , the original angle is:
2. Use the symmetry of the fold UR to find the angle $\angle QRU$.
When the corner containing is folded along the line , the original angle is divided into three parts: the folded angle , the overlapping region underneath (which is also equal to due to folding symmetry), and the remaining unfolded angle shown in Figure 2.
Thus, the folding relation gives:
AI 分析,可能出错
用 AI 批改,圈出写错的那一步,并自动将你的薄弱点存入错题本,形成你的错因库。
同一知识点的其他题
- 1已知四边形ABCD,从下列条件中:(1)AB∥CD;(2)BC∥AD;(3)AB=CD;(4)BC=AD;(5)∠A=∠C;(6)∠B=∠D.任取其中两个,可以得出“四边形ABCD是平行四边形”这一结论的情况有( ) A. 4种 B. 9种…
- 2在四边形中,已知…
- 3在下图中,ABCD 是一个梯形,且 AD = BC。 根据所给信息,以下每个陈述要么是正确的,要么是错误的,要么是无法确定的。请在每个陈述对应的空格内打勾()以表示你的答案。 | 陈述 | 正确 | 错误 | 无法确…
- 4在四边形ABCD中,对角线AC,BD交于点O,OA=OC,OB=OD,添加一个条件使四边形ABCD是矩形,那么所添加的条件可以是 ___ (写出一个即可).
- 5关于长方形和平行四边形的共同特点,有如下一些说法: ①对边平行;②对边相等;③四个角的和是360°;④都是轴对称图形 以上说法正确的是( ) A. ①②和③ B. ①②和④ C. ①③和④ D. ②③和④