A ladder 25 feet long is leaning against a

问题单项选择题

A ladder 25 feet long is leaning against a wall that is perpendicular to level ground. The bottom of the ladder is 7 feet from the base of the wall. If the top of the ladder slips down 4 feet, how many feet will the bottom of the ladder slip ？（）

A．4

B．5

C．8

D．9

E．15

答案

参考答案：C

解析：

根据勾股定理可得在未滑动之前，梯子的垂直高度为：

[*]英尺

顶部向下滑4英尺，则梯子的垂直高度为

20英尺，则梯子距墙根的距离为：

[*]英尺，所以梯子底部将滑动15-7=8英尺。