Solution of Equations

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Solution of Equations
Example Problem
Desire to find the temperature (T) that
corresponds to a desired pressure, P
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Method 1
You do the algebra to rearrange the equation
Then substitute for A, B, C, P (without units!)
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Method 2
Let Mathcad do the algebra for you
Put the T in the blue edit box, click Symbolic
/ Variable / Solve
Copy / paste the solution to a variable
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Method 3
Solve the problem approximately using the
root function in Mathcad
This function takes an initial guess at the
solution and numerically finds a root. Good
for finding a single root of a non-linear
function
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Method 3
For acetone, with P in mm Hg and T in C, A, B, C
are
A 7.02447 B 1160.0 C 224.0
Desire T where P 760 mm Hg
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Method 3
A 7.02447 B 1160.0 C 224.0
Pdes 760
Define the pressure function
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Method 3
Guessestimate a T
Tg 76
Use the root function
T root(Pdes-P(Tg),Tg))
T 55.946
Root drives the first argument to zero by
adjusting the second argument.
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Method 4
Solve block or Given / find block Note
Given Find are keywords in Mathcad!
Define all variables, including guesses for the
unknowns
Start with Given keyword Type equations using
(ctrl ) sign. Close with find (list of
unknowns)
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A 7.02447 B 1160.0 C 224.0
Pdes 760
Tg 76
Given
Solve block
T find(Tg)
T 55.946
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Method 5
Plot the data and solve graphically.
A 7.02447 B 1160.0 C 224.0
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Method 4
Can have multiple unknowns in solve block
S1 1L S2 0.5L S3 1L S4 0.5 L
Given
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Method 4
Find(S2,S3,S4)
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