Page 2 of 3 FirstFirst 123 LastLast
Results 16 to 30 of 41
Like Tree6Thanks

Math Help - sketching curve graph

  1. #16
    MHF Contributor MarkFL's Avatar
    Joined
    Dec 2011
    From
    St. Augustine, FL.
    Posts
    1,988
    Thanks
    734

    Re: sketching curve graph

    You have a positive sign on both sides of the critical value, and since the second derivative is a linear function with positive slope, we know it must go from negative to positive across the critical value. You found the correct value, I just wanted you to be aware of the change of sign of the second derivative. In fact, if the sign does not change, then you do not have a point of inflection.

    If you are asked for the inflection point, then you need the y-value, so plug the critical number into the oriinal function to get the y-coordinate of the inflection point. What does the sign of the second derivative on either side of the critical value tell you about concavity?
    Follow Math Help Forum on Facebook and Google+

  2. #17
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    the critical number would be the -2/3? i plug that into the original equation and obtain the y-value?
    Follow Math Help Forum on Facebook and Google+

  3. #18
    MHF Contributor MarkFL's Avatar
    Joined
    Dec 2011
    From
    St. Augustine, FL.
    Posts
    1,988
    Thanks
    734

    Re: sketching curve graph

    Yes, this will give you the point on the curve where concavity changes.
    Follow Math Help Forum on Facebook and Google+

  4. #19
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    ah, i see. ok i will continue this problem in the morning, thank u for ur help, will probably need more of it in the morn.
    Follow Math Help Forum on Facebook and Google+

  5. #20
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    ok this is what i got...

    https://www.dropbox.com/s/y9fckjmulj...2012.03.32.jpg

    this is my inflection point, right?

    what do i do next??
    Last edited by noork85; May 4th 2013 at 08:13 AM.
    Follow Math Help Forum on Facebook and Google+

  6. #21
    MHF Contributor MarkFL's Avatar
    Joined
    Dec 2011
    From
    St. Augustine, FL.
    Posts
    1,988
    Thanks
    734

    Re: sketching curve graph

    Yes, your inflection point is \left(-\frac{2}{3},-\frac{20}{27} \right).

    Now, what can you say about concavity?
    Follow Math Help Forum on Facebook and Google+

  7. #22
    Super Member
    Joined
    Mar 2010
    Posts
    980
    Thanks
    236

    Re: sketching curve graph

    Quote Originally Posted by Prove It View Post
    Use the Quadratic FORMULA
    Yes, the quadratic formula. Sorry about that.

    - Hollywood
    Follow Math Help Forum on Facebook and Google+

  8. #23
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    now i plot the points on a number line and determine the trend before after and in between??
    Follow Math Help Forum on Facebook and Google+

  9. #24
    MHF Contributor MarkFL's Avatar
    Joined
    Dec 2011
    From
    St. Augustine, FL.
    Posts
    1,988
    Thanks
    734

    Re: sketching curve graph

    Let's review what you need to do:

    a) find where f(x) is increasing/decreasing
    b) where it is concave up/concave down
    c) local max/min
    d) and then finally sketch the curve of the graph

    a) You have done this, but can you formally give the intervals where the function is increasing/decreasing?

    b) you have the information to answer this, can you state it?

    c) you have the information to answer this, and two ways to identify the nature of the extrema...can you show this? Can you give the points and state whether they are maxima or minima?

    d) I would also find the intercepts, then along with the previous steps, you have enough information to accurately sketch the graph.
    Follow Math Help Forum on Facebook and Google+

  10. #25
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    how do i find the intercepts? im sorry if its obvious, but im just finding all of this so very confusing right now.
    Follow Math Help Forum on Facebook and Google+

  11. #26
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    Follow Math Help Forum on Facebook and Google+

  12. #27
    MHF Contributor MarkFL's Avatar
    Joined
    Dec 2011
    From
    St. Augustine, FL.
    Posts
    1,988
    Thanks
    734

    Re: sketching curve graph

    To find the x-intercepts, set f(x) = 0 and solve for x. You should find 3 roots, and this function factors nicely.

    To find the y-intercept, let x = 0, and so it will be (0,f(0)).

    What do you find?
    Follow Math Help Forum on Facebook and Google+

  13. #28
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    im doing this to the original function or to f"?
    Follow Math Help Forum on Facebook and Google+

  14. #29
    MHF Contributor MarkFL's Avatar
    Joined
    Dec 2011
    From
    St. Augustine, FL.
    Posts
    1,988
    Thanks
    734

    Re: sketching curve graph

    To the original function, as this is the curve you are being asked to sketch.
    Follow Math Help Forum on Facebook and Google+

  15. #30
    Member
    Joined
    Mar 2012
    From
    nyc
    Posts
    120
    Thanks
    1

    Re: sketching curve graph

    Follow Math Help Forum on Facebook and Google+

Page 2 of 3 FirstFirst 123 LastLast

Similar Math Help Forum Discussions

  1. curve sketching!! help!
    Posted in the Calculus Forum
    Replies: 2
    Last Post: March 27th 2013, 07:08 PM
  2. Curve Sketching
    Posted in the Calculus Forum
    Replies: 2
    Last Post: August 22nd 2009, 11:33 AM
  3. Curve Sketching
    Posted in the Calculus Forum
    Replies: 1
    Last Post: August 20th 2009, 05:37 PM
  4. Curve Sketching
    Posted in the Calculus Forum
    Replies: 4
    Last Post: April 27th 2009, 02:24 AM
  5. Curve Sketching
    Posted in the Calculus Forum
    Replies: 3
    Last Post: March 6th 2008, 06:18 AM

Search Tags


/mathhelpforum @mathhelpforum