TI-83 Question

  • Thread starter cscott
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  • #1
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Main Question or Discussion Point

With my buddies TI-83 I've plotted a cubic function but am wondering how I can find the x value for a given y value.
 

Answers and Replies

  • #2
tmc
289
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Plot both f(x), the cubic, and g(x)=k, the constant function.

On top of "Trace", click on "Calc."

Go through the menu, look for intersect, and follow the instructions.

(The menu titles might not be exact, I dont have one in front of me)
 
  • #3
782
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I'm not sure if I totally follow but I assumed k = "y value". In my case this was 10^12. I don't really know what the intersect function is asking by "first curve?", "second curve?" and "guess?", but I clicked past them. With lower numbers it seems to work but with 10^12 I get "ERR: NO SIGN CHNG"
 
  • #4
478
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While viewing the graph, click "2nd" then "Trace" to bring up the Calc menu. Select "Value" and enter the x value for which you want the y value. You don't use "Intersection" unless you want the point at which two or more curves intersect and from what you're saying there's only one curve.
 
  • #5
782
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z-component said:
While viewing the graph, click "2nd" then "Trace" to bring up the Calc menu. Select "Value" and enter the x value for which you want the y value. You don't use "Intersection" unless you want the point at which two or more curves intersect and from what you're saying there's only one curve.
I want to do the opposite of what you described! I need the x value for a given y value. Thanks anyway.
 
Last edited:
  • #6
478
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Oh, there is no way that I know of using the original graphing software on the TI-83 to do that. I suppose the reason is because there can be multiple x values for a single y value in a function, not the other way around.
 
  • #7
tmc
289
1
sure he can, simply by doing it my way...

Basically, he wants to solve for f(x)-k=0. So he can either plot f(x)-k, and look for where it crosses the x-axis (I dont remember if a function does that), or make two curves, f(x) and k, and find the x-coordinate of their intersection. Their intersection is where f(x)=k.

Another way would be to go into the solver (i dont remember where it is to be honest, hopefully you know...), which solves equations for you.
 
  • #8
782
1
tmc said:
sure he can, simply by doing it my way...

Basically, he wants to solve for f(x)-k=0. So he can either plot f(x)-k, and look for where it crosses the x-axis (I dont remember if a function does that), or make two curves, f(x) and k, and find the x-coordinate of their intersection. Their intersection is where f(x)=k.

Another way would be to go into the solver (i dont remember where it is to be honest, hopefully you know...), which solves equations for you.
Yes, this worked. Thanks!
 
  • #9
478
2
tmc said:
sure he can, simply by doing it my way...

Basically, he wants to solve for f(x)-k=0. So he can either plot f(x)-k, and look for where it crosses the x-axis (I dont remember if a function does that), or make two curves, f(x) and k, and find the x-coordinate of their intersection. Their intersection is where f(x)=k.

Another way would be to go into the solver (i dont remember where it is to be honest, hopefully you know...), which solves equations for you.
I understand where you're coming from now. That's a nice skill. I'll have to try that out sometime. :)
 

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