# How to find dy/dt and dx/dt in ti84?

I know how to find dy/dx from a point, but how can I find dy/dt and dx/dt from a point?

Please help me...my exam is in a few hours, and this is the last thing I need to learn

Mark44
Mentor
Do you mean "find dy/dx at a point"? If so, you should be able to find dy/dt and dx/dt at a point if you have the formulas for x and y as functions of t.

Yes, I mean at a point. I wasn't given formulas...just points. I'll post an example when I get back home.

equation: y = sqrt(x)

find: a) dy/dt when x = 4
b) dx/dt when x = 25

given: dx/dt = 3

b) 20

I want to know how I can plug in the answers to make sure that they're correct. My exam is multiple choice and I don't have to show any work..

Mark44
Mentor
For a, using the chain rule, dy/dt = dy/dx * dx/dt
dy/dt|x = 4 = dy/dx|x = 4 * dx/dt|x = 4

You're given dx/dt = 3. Can you find dy/dx and then evaluate it when x = 4?

For b, I don't think you have given enough information.

Thanks for the help..now I will ace this exam for sure!