A ballon is rising from the ground. When it is 30 meters above the ground, it is rising at a rate of3 meters per second. An observer is on the ground 40 meters from the point where the balloon originated.
At what rate is the balloon moving away from the observer at this moment when the balloon is 30
meters above the ground? Include units in your answer.
这是一道AP calculus中的经典题目,已经给出解答。如果还有不明白的,可以继续追问。