Can you help him out?

Classical Mechanics Level 4

From point $$A$$ located on a highway, one has to get by car as soon as possible to point $$B$$ located in the field at a distance $$l$$ from the highway. It is known that the car moves in the field $$\alpha$$ times slower than on the highway. At what distance from $$D$$ one must turn off the highway directly to B to reach there in the least of the time.

Details:

• $$l =$$ 500 m
• $$\alpha = 3$$
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