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

  1. Oct 5, 2009 #1
    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
     
  2. jcsd
  3. Oct 5, 2009 #2

    Mark44

    Staff: 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.
     
  4. Oct 5, 2009 #3
    Yes, I mean at a point. I wasn't given formulas...just points. I'll post an example when I get back home.
     
  5. Oct 5, 2009 #4
    equation: y = sqrt(x)

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

    given: dx/dt = 3

    answers: a) 3/4
    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..
     
  6. Oct 5, 2009 #5

    Mark44

    Staff: 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.
     
  7. Oct 5, 2009 #6
    Thanks for the help..now I will ace this exam for sure!
     
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