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# Related rates (Pythagorean theorem)

AP.CALC: CHA‑3 (EU), CHA‑3.E (LO), CHA‑3.E.1 (EK)
You might need: Calculator

## Problem

Two cars are driving away from an intersection in perpendicular directions.
The first car's velocity is 5 meters per second and the second car's velocity is 8 meters per second.
At a certain instant, the first car is 15 meters from the intersection and the second car is 20 meters from the intersection.
What is the rate of change of the distance between the cars at that instant (in meters per second)?