Question about Texas Instruments TI-89 Calculator

When i integrate the function given by the guidebook, x*sin(x), it gives me the answer as -2572.13 instead of sin(x) - x*cos(x). I type it in as (integrate symbol)(x*sin(x),x). No limits, so it really shouldnt be able to express it numerically. Any ideas?

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• SkylineNXS Dec 27, 2008

I found the answer myself actually. If anyone wants to know, if there is a value stored in the variable you are using to integrate, it will produce an undesirable answer.

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• Texas Instru... Master

Hello,
Clear all variables [F6] [ENTER]
Here is a screen capture of the display for your integral.

Hope it helps

Posted on Sep 13, 2009

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Posted on Jan 02, 2017

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### Is it possible to find out integral in TI-83 Plus?

Yes, if you want a numerical answer. Use the fnInt() function in the MATH menu.

No, if you want a symbolic answer.

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### TI89 is giving wrong answer for the integral of sec(x). Please help. It gives the answer as: ln[ |cos(x) / (sin(x)-1)| ] when it should be ln[ |(sin(x)-1) / cos(x)| ]. Why is it giving the wrong...

Hi danagasta,

If my last instructions did not work then you need to reset your RAM. You are missing the negative sign and, I have no idea where you got the absolute value inside the brackets.
Yes, the absolute value are used in books and, on integral tables but, I can asure you that the Ti 89 should not have produce them in this answer.

I'll stand behind that In( -cos(x) / (sin(x)-1)) is the correct answer. You can go ahead and simplify after the calculation to get the answer you want but, that is the good answer that Ti 89 is going to give you for the integral of sec(x).

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I was not able to come up with any of the 3 answers MiB8888 did on my Ti 89. I am not saying that they are not good answers, they are book and integral tables answers. You are not going to get them on the Ti 89.

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Sorry to disappoint you but the Casio FX-9750Gplus does not handle symbolic calculations. It does not have a Computer Algebra System or CAS. It can however calculate the numerical integration of a function between two limits, as well as the first and second derivatives of a function at a given point.

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Yes. Look in the calculus menu (2nd [CALC]). You'll find nDer, der1, and der2 for numerical differentiation and fnInt for numerical integration.

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Hello,
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Hello,

I assume that by anti-derivative you mean the integral. I believe that you can only calculate definite integrals with this calculator. A definite integral requires that you specify the function e.g ln(x), the variable, x, the numerical value of the lower limit, 0.5 and the numerical value of the upper limit , say 2.
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Hope it helps

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Hello,
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Hope it helps

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