Why Doesn't My TI-89 Solve Inequalities Correctly?

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    Calculator Ti-89
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Discussion Overview

The discussion centers around the functionality of the TI-89 calculator in solving inequalities, specifically the example of solving the inequality x^2 < 1. Participants explore various experiences and suggestions regarding the calculator's capabilities and settings.

Discussion Character

  • Technical explanation, Debate/contested, Meta-discussion

Main Points Raised

  • One participant expresses frustration that the TI-89 does not return the expected solution for the inequality x^2 < 1 when using the solve function.
  • Another suggests checking the calculator's setup and clearing variables to ensure that x is not stored as a different value.
  • A different participant claims that the TI-89 cannot solve inequality equations and recommends separating the inequality into two equations to solve them individually.
  • One participant shares a negative opinion about the TI-89, citing a friend's claim that it does not handle inequalities well and is not worth the cost.
  • In contrast, another participant reports that their TI-89 Titanium successfully solves inequalities, indicating a possible difference in models or versions.
  • A later reply proposes an alternative method for solving the inequality using the sign function and factoring.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the TI-89's ability to solve inequalities, with some asserting it cannot while others claim it can. The discussion remains unresolved regarding the effectiveness of the calculator for this purpose.

Contextual Notes

There are indications of potential limitations related to model differences, user setup, and the specific functions available in different versions of the TI-89.

TSN79
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I'm having some trouble solving inequalities with the TI-89. Let's say that I want to solve x^2&lt;1 The answer should be &lt;-1,1&gt;, if I type in solve(x^2<1,x), but that's not what I get. It only returns the inequality itself just as I typed in. What's wrong??
 
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i will have to check the set up but if its all entered correctly make sure you clear your varables so you don't have x stored as something
 
I don't think that the TI-89 will solve inequality equations. You'll have to separate the inequality into two separate equations and solve them separately.

If the TI-89 does have this function, I am unaware. Just checking my manual it doesn't look like it.
 
TI 89 is pretty complicated. I had a similar problem and a Person I know that works a t Texas Instrument Company that makes calculators claims it doesn't do inequalities and is a ripoff for what it seems. aerognr is right.good Luck though!:)
 
This is quite surprising to me because I have a TI-89 Titanium and it can easily solve inequalities. Writing your original query I got: -1<x<1. I was under the impression that the CAS was identical, but apparently they upgraded it.
 
try :

solve(sign(factor(x^2-1))=-1,x)
 

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