HP 35S EQN solve only finding one solution

09252017, 08:56 PM
Post: #1




HP 35S EQN solve only finding one solution
Is anyone else having this problem?
Try a simple equation with two possible solutions for X, e.g. X^24=0. My 35S seems to only be able to find one solution (2), while my 32SII finds either 2 or 2, depending on my starting values. I do this exactly the same for both; if I store negative values for x and in the x register, then 32SII finds the negative solution of 2, while positive gives 2. But 35S finds only 2, seemingly no matter what I do. 

09252017, 09:21 PM
Post: #2




RE: HP 35S EQN solve only finding one solution
(09252017 08:56 PM)Trond Wrote: Is anyone else having this problem? Yes, the 35s is far more intelligent than the 32SII in this regard. Since X only occurs once in the equation it can provide a symbolic (!) solution: x²–4 = 0 => x = √4 which is +2 for the 35s. Just the same as if you had pressed 4 √x. That's why a solution is returned immediately, regardless of the two initial guesses in the variable X and the stack's xregister. Of course you can also solve without this feature: simply add another X somewhere, e.g. by a simple X^2 + 0xX – 4. The "=0" part is not required. Now 0 STO X –5 SOLVE X returns 2. You will also notice that it takes a short moment before the solution is displayed. Just because now the result is not calculated directly but – as usual – approximated by iteration. Dieter 

09252017, 09:36 PM
Post: #3




RE: HP 35S EQN solve only finding one solution
Ah, I was wondering if it was doing that, because entering initial guesses that were far off from the solution did not make it take any longer to solve it. Thanks!


09252017, 09:58 PM
Post: #4




RE: HP 35S EQN solve only finding one solution
I think the 35S solver goes for the "direct" solution if there is one, i.e., square root (4) = +2.
If the equation is more complicated such as how Dieter suggests :) then it is forced to avoid the quick, direct solution. 

09252017, 11:34 PM
Post: #5




RE: HP 35S EQN solve only finding one solution
That does seem to be the case. I tried adding "+0xX" and that made the calculator start searching out different solutions, just like the 32SII.
I'm sure they had a reason to add this solution to the 35S, but I find it a bit counterintuitive. Maybe to avoid the search getting stuck if there is an obvious solution? Still, I like my 35S, so it's good that I found out why it behaves like this. 

09262017, 01:12 PM
Post: #6




RE: HP 35S EQN solve only finding one solution
Good to know


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