Question

下图中的十二个五连方中，有多少个至少有一条对称轴？

How many of the twelve pentominoes pictured below have at least one line of symmetry?

$3$

$4$

$5$

$6$

$7$

答案：D

知识点：对称性系统列举

难度评级：1120

解答：

逐一检查这些五连方的反射对称性，恰好有六个至少有一条对称轴：直条形、十字形、T 形、U 形、V 形和 W 形。其余六个都没有对称轴。

所以正确答案是 D。

Checking each pentomino for a reflection line, exactly six have at least one: the straight bar, the plus, the T-shape, the U-shape, the V-shape, and the W-shape. The remaining six have no line of symmetry.

Thus, the correct answer is D.

2001 AMC 10 第 5 题

答案：D

难度评级：1120

解答：

其他年份的第 5 题