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

1. ## 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.

2. ## 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.

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.

4. ## 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)