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# Finding unknown values within matrices

## Finding unknown values within matrices

(OP)
Good morning all.

I'm having the following problem:

I'm trying to find given pressures at which a resultant force will equal 0lbs, however, the two pressures that affect the resultant force act in different directions but are related to each other. To simplify my problem, I am trying to achieve values for P1 below.

F-((A1*P1)-(A2*P2))=0

where:
A1= 10in^2
A2= 5in^2
F= matrix with 6 rows, 1 column (known values say 100-600 lbs)
P2= P1-300psi ( will be a matrix with 6 rows, 1 column as a result of P1)

P1 must therefore be a matrix with 6 rows and 1 column.

I have tried using the given and find method and the soln but they don't seem to work.  Finding P1 for all six values of F would maybe not be too hard to do individualy however, I'd like to learn how to do it in one go.  I have tried MathCad books but still haven't found an example like this.

### RE: Finding unknown values within matrices

Since you can solve it in (basically) one line I am tempted to think that you are either deliberately or accidentally trying to solve it some more difficult way.

DO you want the obvious solution?

P1:(F+300*A2)/(A1+A2)

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

### RE: Finding unknown values within matrices

(OP)
Yes that'll be it!!

I've spent so long looking at it on the MathCad screen which is covered in matrices and funtions that contain umpteen terms that I was confusing myself to think it's more complicated than it is.

Looking at the original post it is actually quite obvious I'll take it as a lesson learned to use a pen and paper and simplify things right down in the future.  Why It didn't click in my brain as I typed it out I don't know?

Thanks for pointing that out.

### RE: Finding unknown values within matrices

Big hint, I typed the LHS of your equation in and pressed 'solve for' in the symbolic menu, that gave the RHS of the equation above, with one obvious simplification.

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

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