关于透镜的一个问题.原题为英文.

关于透镜的一个问题.原题为英文.
原题：The image of an object formed on a screen by a convex lens has height A.By moving the lens towards the screen,it is found that there is a second lens position at which another image of height B is formed on the screen.The height of the object is
根号(AB) 为什么?
翻译：一个物体通过凸透镜投射到屏幕上的像高度是A,向屏幕方向移动凸透镜,直到物体的像高度是B,求物体的高度.