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ptc-17390381-Visitor
1-Visitor
January 14, 2022
Question

Problem solving a simplle equation with sin ?

  • January 14, 2022
  • 5 replies
  • 5488 views

A simple problem wich worked fin in Prime 6 and doesnt in Prime 7.

In the first line, a simple equation is solved (it's a linear equation!) - all works fine ...

Then some constants where defined and a equation of the same type is to be solved => won't work, after a very long time there is some message, that there is not enough memory (again, to solve a linear equation!!).
If one first calculates the left side of the equation, it works ....
Whats wrong here? Prime error or mine .....

ptc1739038_0-1642168167446.png

 

 

5 replies

P
ptc-17390381-VisitorAuthor
1-Visitor
January 14, 2022

ptc1739038_0-1642168250666.png

 

C
ChrisKaswer16-Pearl
16-Pearl
January 14, 2022

It appears you need to add the "deg" unit identifier to your angles and it will work:

ChrisKaswer_0-1642168621332.png

 

P
ptc-17390381-VisitorAuthor
1-Visitor
January 14, 2022
Thanks ….
But it should work also in the other form ….
L
LucMeekes23-Emerald IV
23-Emerald IV
January 14, 2022

In general it works better to reverse the process. First solve the equation, then fill in the numbers:

LucMeekes_0-1642169607764.png

Note that Prime symbolics doesn't normally work with units...

 

Success!
Luc

P
ptc-17390381-VisitorAuthor
1-Visitor
January 14, 2022
Thanks, but you cannot tell pupills of age 15 to define a function with 3 variables
L
LucMeekes23-Emerald IV
23-Emerald IV
January 14, 2022

That may be true, I can't remember if I was up to such math at that age.

But I'm sure you can tell them to NEVER add a unit to the symbol of a variable. Units should only be added to values...

 

Success!

Luc

W
Werner_E25-Diamond I
25-Diamond I
January 14, 2022
@ptc-1739038 wrote:

A simple problem wich worked fin in Prime 6 and doesnt in Prime 7.

No, thats wrong. What you tried doesn't work in Prime 6 either!

Main reason is that the unit deg is only known to the numeric, but not to the symbolic engine.

You may (re)define "deg" yourself to make it known to the symbolics,too, and what you tried to do will work OK

Werner_E_1-1642180417397.png

!!!BUT ..... what you did is a mathematical and pedagogical disaster! An absolute no-go! The same applies as Luc already said to your approach of adding a unit to an already defined variable. Never do so!
You define an angle to be 85.2 but you mean 85.2 °!! Thats a big difference! Defining alpha to be 85.2 means it to be 85.2 radian per definition.

So the correct way sure is to define the variables with their correct units and while you are doing this you may also assign a unit to l which obviously should be a length:

Werner_E_2-1642180642710.png

You may also use the numeric "root" function or a (numeric) solve block to find x, but what was said concerning variables and units still applies here, too, of course.

 

    P
    ptc-17390381-VisitorAuthor
    1-Visitor
    January 16, 2022

    " ..... what you did is a mathematical and pedagogical disaster! "
    Nice forum, one ask for help and gets insulted ... but the joke is on you, this is the work of a student, so basically you shamed a 15 year old. Kudos.
    "No, thats wrong. What you tried doesn't work in Prime 6 either!"
    I think it has, and most of the time it works in Prime 7 to. I think thats why they used it in the first example. Here a working one

    ptc1739038_0-1642316839222.png

    And how a missing unit can cause the symbolic engine into an "Memory Overflow Error" is strange ...



    P
    ptc-17390381-VisitorAuthor
    1-Visitor
    January 16, 2022

    The "solution" with all the units doesnt work here either:

    ptc1739038_1-1642317682569.png

    What a the correct setttings here:

    ptc1739038_2-1642317769454.png

    I tried it with units on and units off in symbolic math -> no change in behavior ...

     

     

      V
      24-Ruby IV
      ValeryOchkov24-Ruby IV
      24-Ruby IV
      January 16, 2022

      sinsin.png

      W
      Werner_E25-Diamond I
      25-Diamond I
      January 17, 2022
      @ValeryOchkov wrote:

      sinsin.png

      Yes, thats what Luc suggested in his first reply to solve the equation symbolically. But to make it useful to get a numeric result later it would mean that you have to turn it in a function of three arguments and this idea was rejected by the OP because he felt that this approach would not be appropriate for his students/pupils.

      Sure the symbolic SHOULD be able to provide a solution for this simple equation even when the variables are already assigned values and even with the approach which was posted initially (adding the degree "unit" to the variable in the equation). For reasons I can't explain the symbolic sometimes chokes on this equation and while playing around (in Prime 6) I also experienced the problem that the symbolic will run "endless" without returning an solution. I would call it a strange bug (and it has nothing to do with the new symbolic engine, it also happened when I used the legacy engine).

        P
        ptc-17390381-VisitorAuthor
        1-Visitor
        January 24, 2022

        Where do I report this as a bug ?

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