After reading this forum for about three or four years I now decided to join this community, so this is my very first post here. Hope I'm doing everything right. :-)

I'd like to discuss a special feature of the 35s (and possibly other HP-calculators with HP Solve) that I haven't seen mentioned yet. It's about the way the Solver handles equations while it tries so solve for a given variable.

Consider the following equation:

A^2 + 2xAxB + B^2 = 8

Let's keep it simple and assume B = 0. This leads to A = +/- sqrt(8) = +/- 2.8284...

After providing two guesses in A and x like...

0 STO A 9

...and starting Solve A, leaving B=0, the 35s is SOLVING for a few seconds and finally returns the expected result A=2.82842712475 in x. The y-register holds the second-best result 2.82842712474, indicating that the result that solves this equation exactly is somewhere between these two values (which in fact is the case). Changing the initial guesses to 0 and -9 returns the same values with a negative sign. So far everything works like expected.

Now let's try the same equation, just simplified to

(A+B)^2 = 8Again we provide two guesses 0 and 9, start Solve A and let B=0. What happens now? The 35s

*immediately*(!) comes back with A=2.82842712475, both in x and y - there are no two adjacent solutions, just one single value: the one the 35s returns for sqrt(8).

Now let's try to find the negative solution with the same negative guesses as before: 0 and -9. And again, the 35s

*immediately*returns the same positive (!) solution as before. For any intial guess this is the only result it returns.

Okay, what happens here? It seems to be something like this: If the 35s realizes that it can easily solve an equation because the desired variable appears only once, it

*transforms*this equation symbolically, in this case giving A = sqrt(8) - B. In all other cases the usual iterative numeric approach is used.

Please forgive me if this is old news, but I was a bit puzzled when I found this... er... "special feature" of the 35s. :-)

Regards,

Dieter