# How Near Can They Be?

Calculus Level 3

Two boys (let them be Black and Red) start walking on two roads with a constant speed of 5m/s and 10m/s respectively. Find the shortest distance between the two boys.

Details:
- The roads make a right angle.
- They are 10m apart at the start.
- Red starts at the intersection.
- The directions in which they move are shown by arrows in the diagram.
- They can only walk on the roads.

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