Author Topic: AP calculus help.... Please  (Read 412 times)

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Offline Assan

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AP calculus help.... Please
« on: October 22, 2014, 09:23:45 pm »
Okay I have a problem in my homework I can't figure out how to do:

If a function f(x) is increasing what must be true about f '(x)?

I get that if it is increasing then f '(x) is positive but I can't get how to do the second part:

Use this idea to determine algebraically where f(x) = 3x2 - 3x + 1 is increasing.

If you can help I would appreciate it.  :fox-:):
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Offline Jethro

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Re: AP calculus help.... Please
« Reply #1 on: October 23, 2014, 11:36:23 am »
Take the derivative of that.


Remember, the derivative of a function is the slope of the function. 

Okay so deriv is   6x-3

Set that equal to zero and solve for the critical points.  You get 1/2     Now you have to pick any number above and below 1/2 for x  (Do 0 and 1 to be easy).
  If your answer is positive, that means it is increasing. Negative is decreasing.

6(0)-3 =   -3   So up until 1/2 your function is decreasing.
6(1)-3 =   3   After 1/2 your function is increasing.

Also, if you plugged your original function into a graphing calculator you could easily just see where it's decreasing/increasing.

Offline Assan

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Re: AP calculus help.... Please
« Reply #2 on: October 23, 2014, 01:12:25 pm »
Thanks I just couldn't figure out how to do it.

PS. We were not supposed to use our calculators for this assignment.
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