How to easily and accurately find intersection points on graphs
10-02-2018, 12:10 PM
Post: #1
 JDW Senior Member Posts: 382 Joined: Jun 2016
How to easily and accurately find intersection points on graphs
My daughter was working on her high school math homework this evening using her Prime. She typed in the following set of 4 inequalities:

When she pushes the Plot button, it draws the graph and she needs to find the 3 intersection points. I just told her to use the crosshair and circular movement button to jump to the points, but she complains that (a) moving the cursor around takes too long (it does), and (b) even when you move the crosshair over the intersection point the x & y data is not perfectly what it should be (it isn't). For example, if you look at the crosshair in the graph below, it should be x=0 & y=1.2 on that intersection point, but when using the Prime's crosshair manually I can only manage x=0.0035 & Y=1.19925. Sure, she could mentally just round off, but sometimes you want a precise number in cases where the intersection point is not so easy to determine by rounding.

Here's the second intersection point:

And here's the 3rd intersection point, which is supposed to be x=0 & y=0:

So what's the easy and fast way to jump to the exact intersection points on the graph using the Prime?

Thanks.
Post: #2
 roadrunner Member Posts: 292 Joined: Jun 2015
RE: How to easily and accurately find intersection points on graphs
Example for the second point:

then

Menu, Trace, Poi, Intersections with..., V2

then

scroll the curser to the corner with the right arrow key.

10-02-2018, 01:58 PM
Post: #3
 JDW Senior Member Posts: 382 Joined: Jun 2016
RE: How to easily and accurately find intersection points on graphs
In other words, there is no fast and easy way! :-(
Post: #4
 roadrunner Member Posts: 292 Joined: Jun 2015
RE: How to easily and accurately find intersection points on graphs
If you make V1 thru V4 equalities:

you can skip the scrolling.

10-02-2018, 10:56 PM
Post: #5
 JDW Senior Member Posts: 382 Joined: Jun 2016
RE: How to easily and accurately find intersection points on graphs
Please know that I appreciate the suggestions. But it’s still a lot of trouble.

My daughter actually showed me an app on her iPad that allowed her to merely tap near an intersection point and it would automatically jump it’s crisshair to the exact intersection point and show the X and the Y values. Since we are allowed to tap on the Prime, it would be nice if the graphing app could be updated to add this great convenience feature. And I would also propose that once you tap and once it jumps the crosshair onto the nearest intersection point, you should then only need to press the circular movement button once to jump to the next contiguous intersection point and press it again to jump to the next intersection point in so on.

Although it is possible to rethink equations as you suggest, there are prudent reasons for the sake of speed and productivity to improve the app.
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