Two cars start moving from the same point. one travels south at 10 mi/h and the other travels west at 70 mi/h. At what rate is the distance between the cars increasing 2 hours later?

Question

hero · Answer

Take derivative with respect to time

anonymous · Answer

take the deriative of x^2 +y^2=z^2?

hero · Answer

yes

hero · Answer

What is x, y and z after two hours?

anonymous · Answer

80?

hero · Answer

x = 20 after two hours
y = 140 after two hours
z = ? after two hours

hero · Answer

you should be good from here. I'm sure you know how to take derviative.

hero · Answer

After that, it's just plug and play

hero · Answer

If not, I can post solution

anonymous · Answer

okay so i got 2x+2y=2z and then i plugged everything in and still got 80 lol

hero · Answer

you didn't take derviative with respect to t

hero · Answer

What you should have gotten was this: 

$$2x \frac{dx}{dt} +2y \frac{dx}{dt} = 2z \frac{dz}{dt}   $$

hero · Answer

and of course dx/dt = 10
and dy/dt = 70

hero · Answer

you should already know x, y, and z

hero · Answer

By the way, you're solving for dz/dt