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Need help with HP 50g

  1. Jan 1, 2009 #1
    I can't find how to do this in the HP 50g manual (probably because the manual is 900 pages and I don't know what to look for) so hopefully someone can help me. I'd like to set my 50g so that it doesn't expand expressions by default. For example, if I tell it to compute [itex]\int{(10x^2-8)^{40} dx}[/itex] it will integrate it but then expand it, which makes it useless for checking integrals like this.
  2. jcsd
  3. Jan 2, 2009 #2
    What's really happening is that the expressions is being expanded before integrating, not after. In your example, there is actually no obvious substitution that can make it easy to integrate with that method; indeed, both Mathematica and my TI-89 will expand it before integrating (and give a large mess as a result). There doesn't seem to be a nice general formula for the result (well, Mathematica can give one that uses hypergeometric functions, but it's not exactly pretty).

    I seem to remember reading that, in general, HP calculators do tend to expand polynomials before integrating, rather than perform a substitution if it's simple enough. I really doubt there's any way to tune how it integrates things.

    As an example: [itex]\int (x + 1)^3 \,dx[/itex]. I'm guessing your calculator gives a result of [itex]\frac14 x^4 + x^3 + \frac32 x^2 + x[/itex]. (I'm not 100% sure; I read this before the 50g came out, but the 50g is fairly similar to the 49G.) However, both Mathematica and my TI-89 give [itex]\frac14 (x + 1)^4[/itex]. Note that this expands to [itex]\frac14 x^4 + x^3 + \frac32 x^2 + x + \frac14[/itex]; the result differs from the other one by a constant 1/4. (Hopefully this demonstrates the importance of the integration constant!)
  4. Jan 3, 2009 #3
    Thanks for the response.

    Yeah I didn't notice that, my example should have been [tex]\int (10x-8)^{40} dx [/tex]
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