Results 1 to 4 of 4

Thread: Ti-89 Titanium: Saving an intersection point. Then using exact(ANS)

  1. #1
    Newbie
    Joined
    Mar 2015
    From
    Berea, Ohio
    Posts
    3

    Ti-89 Titanium: Saving an intersection point. Then using exact(ANS)

    I was having an issue with transferring a data value from the [Graph] app of intersecting curves to the [Home] app on the TI-89 Titanium.

    Previously on my TI-83 Plus would accomplish this task seamlessly.
    Example:

    Y1= 1+sec(x)
    Y2= 3

    [2nd] [Calc] [5] [First Curve] [Second Curve] [Guess]
    Intersection: X=-1.049198

    [2nd] [Quit] [2nd] [ANS]
    Output: -1.049198

    Currently on my TI-89 Titanium:
    Y1= 1+sec(x)
    Y2= 3

    [F5][5][First Curve][Second Curve][Lower Bound][Upper Bound]
    Intersection: X=-1.0472

    Here is where I am lost. Doing [Home] [2nd] [ANS] yields "Error: invalid ans()"


    I would like to get ANY point off a graph and compute it to an exact fraction if possible.

    In this case, I know that the intersection (Approx -1.0472) is exactly (-pi/3) and would like to easily see this.

    So if I get the output 55.7633, I would hope to actually get 71pi/4 and not the decimal approximation. I don't want to receive the approx while not realizing there is an exact form for it.

    Additionally, using exact(-1.0472) does not yield the pi fraction (I realize that the number is irrational and I used an approx, so that's why it gives me a huge decimal)

    So how would I go about
    1- Getting data to transfer from graph to home.
    2- Getting exact pi fractions from the approximations my calculator gives me.

    Thank you for reading this overly long question on a basic problem.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    15,767
    Thanks
    3492

    Re: Ti-89 Titanium: Saving an intersection point. Then using exact(ANS)

    Well, had to dig my old TI-89 (not a titanium) out of the closet and buy batteries, so you owe me a beer.

    When you find the intersection, the values at the bottom of the screen say ...

    xc: -1.047198 yc: 3

    If you go to the home screen and type xc, then hit enter you will see the value for x calculated as the intersection's abscissa. You can store it elsewhere, or leave it in xc (note xc will change if you calculate another intersection, zero, whatever), so I would store it in another register.

    $xc \rightarrow p$

    To get exact fractions with $\pi$, you need to be in auto or exact mode. If the calculator is capable of providing an exact value in terms of $\pi$, it will ... otherwise it will only give a decimal approximation.

    Hope this helps.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Mar 2015
    From
    Berea, Ohio
    Posts
    3

    Re: Ti-89 Titanium: Saving an intersection point. Then using exact(ANS)

    I appreciate your dedication to helping out a stranger.
    The information you provided did yield relief to part of my frustrations, but fell short on another.
    Although, the information you provided is sound, I believe the calculator is what is failing me.

    The intersection of y=1+sec(x) and y=3 sound be -pi/3 (left intersection)
    However, with exact mode on, it still rounds to -1.0472 on the graph screen.
    Using xc, i had hoped to convert it to a fraction over pi.....but I got (-5235987755983/5000000000000) which is far from simply -pi/3.


    I will use the information you provided though, it will be very useful to extract data right from the graph and I am very glad to have got that answer.
    You deserve a beer.
    Last edited by Ryoohki166; Mar 25th 2015 at 07:14 PM.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    skeeter's Avatar
    Joined
    Jun 2008
    From
    North Texas
    Posts
    15,767
    Thanks
    3492

    Re: Ti-89 Titanium: Saving an intersection point. Then using exact(ANS)

    I entered y1(x) = 1 + sec(x) into Y= and used the "solve" feature ...

    solve(y1(x)=3,x)

    the calculator returned the solution ...

    x = \frac{(6 \cdot @n1+1)\pi}{3} \text{ or } \frac{(6 \cdot @n1-1)\pi}{3}

    where @n1 is the calculator's notation for an arbitrary integer (if I remember correctly)
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Exact coordinates of M (The minimum point)
    Posted in the Calculus Forum
    Replies: 11
    Last Post: Mar 18th 2012, 05:03 PM
  2. point of intersection
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: Dec 8th 2008, 07:37 PM
  3. TI-89 Titanium, FINDING AN INTERSECTION
    Posted in the Calculators Forum
    Replies: 7
    Last Post: Oct 9th 2008, 03:40 AM
  4. TI-89 Titanium, FINDING AN INTERSECTION
    Posted in the Calculators Forum
    Replies: 1
    Last Post: Aug 28th 2008, 05:57 PM
  5. Point of intersection
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: Apr 10th 2008, 08:21 PM

Search Tags


/mathhelpforum @mathhelpforum