Задача id13119

The light source is located at a distance of 1.5 m from the screen, on which an enlarged image of the source is obtained using a converging lens. The screen is then moved back another 3 m and an enlarged image of the source is again obtained. What are the focal length of the lens and the size of the source if the image size in the first case is 18 mm, and in the second case 96 mm?

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