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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Mathematical Methods CAS => Topic started by: TrueTears on September 16, 2009, 04:24:59 pm

Title: TI-89 CALC error?
Post by: TrueTears on September 16, 2009, 04:24:59 pm: Eh I typed "solve(sin(3x) = -1 ,x) | $\frac{-\pi}{2} \le x \le \frac{\pi}{2}$ "

And it only comes up with $x = \frac{-\pi}{6}$ ?

But surely $x = \frac{\pi}{2}$ is also a solution?

Is my calc broken?
Title: Re: TI-89 CALC error?
Post by: shinny on September 16, 2009, 05:11:45 pm: CAS's aren't perfect. This will happen quite often (although I'm surprised it happened on a simple trig equation) and really, the only way to prevent it is to graph everything instead, and find the x intercepts.
Title: Re: TI-89 CALC error?
Post by: Gloamglozer on September 16, 2009, 05:15:18 pm: Are you using v 3.10 or v 3.01? Check by pressing F1 in home and scroll down to "About".
Title: Re: TI-89 CALC error?
Post by: TrueTears on September 16, 2009, 05:22:33 pm: Quote from: shinny on September 16, 2009, 05:11:45 pm
CAS's aren't perfect. This will happen quite often (although I'm surprised it happened on a simple trig equation) and really, the only way to prevent it is to graph everything instead, and find the x intercepts.
Yeah I normally do but I was surprised that it got such a simple trig equation wrong... so I thought something must have gone wrong.

Quote from: Gloamglozer on September 16, 2009, 05:15:18 pm
Are you using v 3.10 or v 3.01? Check by pressing F1 in home and scroll down to "About".
Says version 3.10
Title: Re: TI-89 CALC error?
Post by: Gloamglozer on September 16, 2009, 06:35:09 pm: Quote from: TrueTears on September 16, 2009, 05:22:33 pm
Quote from: Gloamglozer on September 16, 2009, 05:15:18 pm
Are you using v 3.10 or v 3.01? Check by pressing F1 in home and scroll down to "About".
Says version 3.10

That should be ok then. I highly doubt it's going to happen to you, but just to check, your calculator is set to degrees mode, yeah?

If so, then as shinny stated above, the calculator cannot be trusted. :)
Title: Re: TI-89 CALC error?
Post by: pHysiX on September 18, 2009, 07:07:19 pm: CAS's can be sooooo deceiving. Man, i had the function [latex]\sqrt{x^3-1}[/latex] and i needed values at 2, 2.5, 3, 3.5 and 4. I did this 10 times: y1(....) where y1(x) is the function. The first 3 times, i got different values. The next day, i did it again and got even more different values and for the last 4 times i did it at uni, i was so p'd off that i just took my friend's values...sorry for rambling but yes, being too reliant on CAS is "no good" (cost me my spesh sac >.>)