求助：GWD 2-6 数学

apply1

Q6: 有图：半圆直径是12ft.

The figure above shows the dimensions of a semicircular cross section of a one-way tunnel. The single traffic lane is 12 feet wide and is equidistant from the sides of the tunnel. If vehicles must clear the top of the tunnel by at least ½ foot when they are inside the traffic lane, what should be the limit on the height of vehicles that are allowed to use the tunnel?

A. 5½ ft

B. 7½ ft

C. 8 ½ ft

D. 9½ ft

E. 10 ft

答案是c, 不知道怎莫做的。

himba

题目不难，关键在于画出图来：

1）隧道截面半圆，直径一给。2）货车截面为一长方形，其顶点不内接，根据题意，应与半圆弧相距半英尺。该长方形长度关于半圆圆心对称。

很容易吧。

apply1

thanks   a    lot  !!!!