Задача 40933.

On the table lay an open book, which is the spine of length L = 50 cm is directed to the desk lamp. The line connecting the top of the page with the thread of the lamp has the same length and at an angle of 60 ° to the table surface. Find the difference of lighting the top and bottom of the page, if the intensity is I = 100 cd.

Detailed solution with a short recording conditions, laws and formulas used in the decision, the withdrawal of the calculation formula and the answer.
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