题目:人立于河边看对岸一根电线杆在水中的像,当人离河岸后退超6米时,就不能看到整个电线杆的像了.人高1.5米,河两岸都高出水面1米,河宽40米,求电线杆高.本题在九九年第三期提供了一种解法.在此,我提出另一种数学解法供参考.解:依题意及平面镜成像性质作此光路图 Subject: People stood by the river and looked at the image of a pole in the water on the opposite bank. When the person retreated 6 meters behind the river bank, he could not see the entire pole. The height of the person was 1.5 meters. Both sides of the river were above the water. 1 meter, the river is 40 meters wide, and the power pole is high. This question provides a solution in the third period of 1989. Here, I propose another mathematical solution for reference. Solution: According to the meaning of the problem and the imaging properties of the plane mirror This light path diagram