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Top Student
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Member Since: ‎10-19-2015
Message 1 of 13 (166 Views)

# Why do you need to be in Radian mode to solve equations symbolically?

Product Name: HP 50G

I typically run my 50G in Degrees mode.     When I try to use the S.SLV/SolveX  function,  it pops up a dialog stating:  Radian Mode On?".   If I select Yes then is will solve for X, otherwise it does not.

Why do you need to be in radian mode to solve a polynomial symbolically?

Thanks,

garbel

NOTE:  Equation was   X^2-2X+1=0   (Tried others)

# Re: Why do you need to be in Radian mode to solve equations symbolically?

garbel wrote:

... Also,  if this [having Radians mode set] was a requirement,  I would expect it be documented some where.   I haven't found it if it is.  If you know where it's documented,  I'd love to see it.

It's in the HP 50g Advanced User's Reference Manual, in the "Flags" section of all the commands that require radians mode to be set, including SOLVE and SOLVEVX. A quick search with a PDF reader reveals that roughly 90 functions in the HP 50g require radians mode to be set.

Also, on page 4-2 (PDF page 426), in the section about the CAS, this appears: "Not only the trigonometry rewriting operations, but some other CAS operations require the angle mode to be set to radians (flag –17 clear), even if it is not immediately obvious that this is so. For this reason, the Flags section of many operation descriptions says that radians mode should be set."

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Teacher
Posts: 86
Member Since: ‎05-30-2013
Message 2 of 13 (137 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

Hello,

My best guess is that since you have not specified that X is a real, then the system assumes that X can be a real or a complex when it tries to solve it.

Therefore, to solve the system, you will need to do complex number powers (square root is power 1/2) and complex number powers are angle dependent...

As I said, my best guess...

Cyrille

I am an HP Employee
Top Student
Posts: 7
Member Since: ‎10-19-2015
Message 3 of 13 (115 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

Hi Cyrille,

I tried equations such  X^2 + 2x + 1 that has real roots and I see the same things.   I tried with the cas   real/complex mode on/off.

I see no reason why it has to be in radian mode to solve for equations such as this.    I assume there is either a good reason that I don't know of or a defect.   Either way it's not a big deal,  I was just playing around.

I typically use my HP Prime but I hate to see my  HP 48G and HP 50G sit around doing nothign so once a month I switch my made calculator so they all get equal time.

I also have a   HP35S but I really dislike it.  I like the keyboard but that's about it.

Top Student
Posts: 7
Member Since: ‎10-19-2015
Message 4 of 13 (113 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

I should also mentioned that I think this is probably one of the first HP50G units so it's probably go old firmware.

I tried getting the revision but the 3 button sequence resets the calculator and prompts me if I want to recover memory no not.   I would have thought the revision would be visible somewhere.

Is the firmware updatable on an HP 50G?

Thanks,

Posts: 309
Member Since: ‎02-04-2014
Message 5 of 13 (106 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

garbel wrote:

I should also mentioned that I think this is probably one of the first HP50G units so it's probably go old firmware.

I tried getting the revision but the 3 button sequence resets the calculator and prompts me if I want to recover memory no not.   I would have thought the revision would be visible somewhere.

Is the firmware updatable on an HP 50G?

The easiest way to get the version number is the VERSION command. Just type it (or execute it from the CATalog).

The most recent version is 2.15. If your version is lower than that, yes, you can update your 50g's firmware. Details & firmware here: http://www.hpcalc.org/details/7097

-Joe-
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Message 6 of 13 (101 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

Thanks Joe,

Looks like it's revision 2.15 so I have the latest.

..

Teacher
Posts: 86
Member Since: ‎05-30-2013
Message 7 of 13 (94 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

Hello,

"I tried equations such  X^2 + 2x + 1 that has real roots and I see the same thing."

You do know that this equation has only real roots. But the CAS does not know that until it tried to solve it. And to solve it, it will have to take the 1/2th power of a number. Since it does not know at this point if the result will be a real or a complex, it will use the generic complex power function to take the 1/2th power, and complex power are angle dependent as they incolve trig functions.

I know that it sounds weired to us, human, as we tend to use specific, "easier" algorythms to solve specific problems for which we know the bounds. But the CAS does not have that luxury, unless you specifically tell it to. This means that the CAS will, by default, use "generic", powerfull, but complex algorythms to solve a problem (to get started because it might allow the programmer to only implement one single algo instead of plenty of specific ones). And here is the result.

Now, in your case, YOU KNOW that this is a polynome, so you could provide the CAS that info and have it use a polynome specific solving algorythm by calling a function like POLYROOT. This would (I think), solve your problem.

Cyrille

I am an HP Employee
Top Student
Posts: 7
Member Since: ‎10-19-2015
Message 8 of 13 (71 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

Hi Cyrille,

Regardless of what has to go on internal,  it shouldn't force you to change modes manually -- it can do that internally if needed to determine a result.

It like saying that given the calculator uses Pi to determine angles,  you have to switch it to radian mode to use pi.

Since I was only playing and HP no longer manufactures the 50G, it's not a big deal.

Also,  if this was a requirement,  I would expect it be documented some where.   I haven't found it if it is.  If you know where it's documented,  I'd love to see it.

I'm sure you can't state anything definitely but I'd be curious if you guys have a Scientific/Engineering Calculator that will replace the 50G?

The Prime is great but it's more directed at Math Students.

Teacher
Posts: 86
Member Since: ‎05-30-2013
Message 9 of 13 (56 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

Hello,

You are correct in saying that the switch to radian should be done internally only and not visible to the user (althrough I am not 100% sure that this would not lead to eroneous results in some cases)... You are right in saying that the documentaiton lacks (remember that the 50g CAS comes from a 3rd party and is itself not well documented:-( )

HP Prime is what we have to replace the 50g so far. I know that this is not exactly what you want to hear but that is the only choice so far.

Honnestly, as a long time HP28s, HP48sx, HP48gx, HP49g, HP50g user, I had little to no problems to move to Prime. The only "draw back" is the lost of a true RPN, but franckly, Prime is so insanely powerfull and fast that it overcomes all these issues. The only time where I trully miss RPN is when I have to do a long series of add/substracts.

Prime also has a quite decent keyboard (especially the latest versions with the new color)

If you have not done it yet, give the Prime a try. We now have free (with some limitation) versions available for all the "stores" (IOs, Android and Windows)...

Cyrille

I am an HP Employee
Posts: 309
Member Since: ‎02-04-2014
Message 10 of 13 (54 Views)

## Re: Why do you need to be in Radian mode to solve equations symbolically?

garbel wrote:

... Also,  if this [having Radians mode set] was a requirement,  I would expect it be documented some where.   I haven't found it if it is.  If you know where it's documented,  I'd love to see it.

It's in the HP 50g Advanced User's Reference Manual, in the "Flags" section of all the commands that require radians mode to be set, including SOLVE and SOLVEVX. A quick search with a PDF reader reveals that roughly 90 functions in the HP 50g require radians mode to be set.

Also, on page 4-2 (PDF page 426), in the section about the CAS, this appears: "Not only the trigonometry rewriting operations, but some other CAS operations require the angle mode to be set to radians (flag –17 clear), even if it is not immediately obvious that this is so. For this reason, the Flags section of many operation descriptions says that radians mode should be set."

-Joe-
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