The grid shows a shaded shape. The dashed line is a mirror.
Which picture shows the reflection of the shape in the mirror?
AA.
BB.
CC.
DD.
答案: C
答案:C(最右一列是竖条,底部的“脚”朝左)
立在旁边的镜子会把图形左右翻转,上下不变。从镜子开始数列数。
竖条在第1列,离镜子4列,所以倒影在镜子另一边、同样离镜子4列的地方:第4列的第1到3行。
底部的“脚”在第2列第3行,离镜子3列,所以倒影在第3列第3行。
为什么其他选项不对
A:这个图形还被上下颠倒了,“脚”跑到了上面。
B:这是原样照搬,没有翻转;镜子里的“脚”应该朝回指向镜子。
D:这是上下翻转,但立在旁边的镜子是左右翻转。
讲解示例 2
The net below is folded to make a cube.
When the cube is folded, which shape is on the face opposite the circle?
AA.
Heart
BB.
Diamond
CC.
Moon
DD.
Triangle
答案: B
答案:B(Diamond,菱形)
把圆形平放在桌上,当作正方体的底面。
心形和月亮都和圆形共用一条边,所以折起来分别成为后面和前面。
星形(连在心形旁边)和三角形(连在月亮旁边)折过来,成为左面和右面。
菱形连在三角形下面,所以会折到顶上,成为顶面。
顶面和底面相对,所以菱形在圆形的对面。
为什么其他选项不对
A(Heart):心形和圆形共用一条边,是相邻的面,不是相对的面。
C(Moon):月亮也和圆形共用一条边,是相邻的面。
D(Triangle):三角形是侧面,它的对面是星形。
讲解示例 3
Wiremu is making a sewing card from a square of paper. The paper is marked in a 4 × 4 grid. Each square is named by its column letter and row number, as shown.
A
B
C
D
1
A1
B1
C1
D1
2
A2
B2
C2
D2
3
A3
B3
C3
D3
4
A4
B4
C4
D4
Fold 1: He folds the right half over onto the left half, along the line between columns B and C.
Fold 2: He folds the top half down onto the bottom half, along the line between rows 2 and 3.
Punch: He punches one hole through all the layers, in the spot where square A3 is.
Wiremu unfolds the paper. Which squares have holes in them?
预览片段有英文和中文字幕,把一张正方形纸对折,剪掉一个角,再讲展开时的黄金法则:剪口会穿过每一层。SelectiveReady应用里的完整课程还讲镜像、旋转、正方体展开图和常见陷阱;课程和应用界面为英文。免费账户可以看一节课程(How and Why Authors Write),其他课程需要付费方案。