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ptc-52606871-Visitor
1-Visitor
September 13, 2013
Question

This variable is undefined

  • September 13, 2013
  • 6 replies
  • 27491 views

Any help appreciated. I sure this has been asked ad infinitum but I can't find the answer.

I want to use Mathcad to assit my child in algebra. At times, I just want to use it instead of pen and paper, for example.

My child may have to solve this simple problem by isolating "x"

5x-7=9

I just want to write this in mathcad and work through the equality. But of course two(2) problems:

1) x appears outline in red as undefined. I've tried preceding it with x:=x and other ideas but nothing works. In fact, in x:=x, the second x has same problem with red outline and undefined error.

2) the "=" causes the problem to solve (if x is defined i.e. x:=2). The solution 3 would appear on the right side of the "=" and I can't type the nine(9).

Well, I'm sure many have seen this before.

Please help as it would be great to do algebra (solving equations manually) using mathcad using the computer where our work can be saved (and double checked by math cad).

Thank you,

DJ

6 replies

R
RichardJ19-Tanzanite
19-Tanzanite
September 14, 2013

We can certainly help, but please post the worksheet. To add an attachment click on "Use advanced editor" at the top right, then if you go to bottom left (OK, illogical, but that's how it works) you can add an attachment.

V
ValeryOchkov24-Ruby IV
24-Ruby IV
September 14, 2013

alg.png

P
ptc-52606871-VisitorAuthor
1-Visitor
September 14, 2013

Thank you much for the answer. Worked Great.

DJ

H
HarveyHensley12-Amethyst
12-Amethyst
September 14, 2013

You can use the Boolean equal sign (ctrl 😃 so the undefined variables won't be in red.

algebra.png

Is that what you want?

P
ptc-52606871-VisitorAuthor
1-Visitor
September 14, 2013

Thank you much for the answer. Worked Great.

DJ

A
arbiter1-Visitor
1-Visitor
September 14, 2013

You could use the <CTRL>= constraint operator instead of the :=. Then, select the x, and use Symbolics|Variable|Solve in M15.

Note that Mathcad will not display the steps for solving equations, so it's relatively limited in this regard.

P
ptc-52606871-VisitorAuthor
1-Visitor
September 14, 2013

Thank you much for the answer. Worked Great.

DJ

A
AlanStevens19-Tanzanite
19-Tanzanite
September 14, 2013

Something like this?

Equals sign.PNG

Alan

Uh-oh! Moderated again, so I guess a dozen identical answers to this will suddenly appear!

P
ptc-52606871-VisitorAuthor
1-Visitor
September 14, 2013

Thank you much for the answer. Worked Great.

DJ

W
Werner_E25-Diamond I
25-Diamond I
September 14, 2013

Whats wrong with using and reading the built-in help??

Chapter "Symbolics and Keywords", subchapter "Solving Equations Symbolically":

"To solve an equation symbolically, type the equation using the Boolean equals sign ([Ctrl] [=]) and either:

Then press [Enter].

If the function contains more than one variable, type a comma after "solve," and then type a comma-separated list of the variable(s) you want to solve for in the placeholder."

symbequ1.png

You did not state which version you use, so I assumed Mathcad 15.

If you use Prime or Prime Express, the help is somewhat more unclear and cumbersome but the information is there nonetheless. You would have installed the help pages locally on your machine, but for Prime the help is available online, too. What you need is here: http://www.ptc.com/cs/help/mathcad_hc/prime2_hc/index.jspx?id=resourceid-131-8CCFC2DB&action=show

P
ptc-52606871-VisitorAuthor
1-Visitor
September 14, 2013

Thank you much for the answer. Worked Great.

DJ

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