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HP35S solve problem  Alessandro Castellani (Italy)  12312011
I'm new in this forum and I have a problem on my 35S: Re: HP35S solve problem  Dieter  12312011 Alessandro, there's nothing wrong with your 35s. You just discovered a feature that is often overlooked: the 35s can solve equations symbolically. It does so if the variable appears only once in the equation.
This also happens in your case. Here, the equation X^2  4or X^2  4 = 0is automatically transformed to X = SQRT(4)This exact solution is then evaluated by the 35s, using its regular functions. So the square root always returns a positive result. This also means that  in such a case  the two initial guesses do not matter at all, they are completely ignored.
If you want the usual numerical solution by successive iteration, simply change the equation a bit so that the variable appears twice: X*X  4or X^2  4 = 0*X All this has been discussed before. For more information and further details, please take a look at this thread. Dieter
Edited: 31 Dec 2011, 11:18 a.m.
Re: HP35S solve problem  Alessandro Castellani (Italy)  01022012 Thank you very much Dieter.
Alessandro
Re: HP35S solve problem  Paul Dale  01022012 How fares the 35S with X! = 6 ?? Variable appearing exactly once but there is no inverse gamma function on the device that I'm aware of.
Re: HP35S solve problem  Norman Dziedzic  01022012 Without using the multiple variable trick in the equation it went for about 40 seconds and I canceled it.
Using the equation
It returned 3.000 (my setting Fix 3) after about 10 seconds.
Re: HP35S solve problem  Dieter  01022012 Well, there are some restrictions so that not all cases with a single appearance of the variable are solved symbolically. For instance, consider periodic functions like sin or cos. An equation like SIN(X) = 0,5will not be solved directly since there is an infinite number of solutions (30, 150, 390, 510, ... degrees). So the 35s will not simply set x = arcsin(0,5) and return 30 degrees.
The case you mentioned X! = 6cannot be solved directly since there is no inverse factorial or inverse Gamma function on the 35s. So the usual iterative approach is applied here. I tried various initial guesses between 0 and 20  the 35s always came up with the correct result x = 3, usually within 4  10 seconds. No tweaking (...+0*X) was required.
Dieter
