       HELP!! Using Solve for Simultaneous Eqns.

• To: mathgroup at smc.vnet.net
• Subject: [mg8338] HELP!! Using Solve for Simultaneous Eqns.
• Date: Sun, 24 Aug 1997 13:24:54 -0400
• Organization: Goldengate Internet Services, Inc.
• Sender: owner-wri-mathgroup at wolfram.com

```I am using these two equations:

convert={power==10voltage×current,voltage==r×current};

to define the conversion from mW/cm^2 to V/m and A/m.

If I use the Solve function for the simultaneous equations with all of
the variables in the list of variables to solve for, I get a message:

Solve::"svars": "Equations may not give solutions for all \"solve\"
variables.

and the result contains two of the four variables in the equations.

I can force the results I am looking for by using three Solve
statements, defining the two variables I know, listing the output
variables I need, in the appropriate statement, and look at the
output, But I think I shouldn't have to do that.

Reduce[convert,{power,voltage,current,r}];

temp=Solve[convert,{power,voltage}];
temp/.{current -->2.82091,r -->377}//N

temp=Solve[convert,{power,current}];
temp/.{voltage -->1063.48,r -->377}//N

temp=Solve[convert,{voltage,current}];
temp/.{power -->30000,r -->377}//N

I would like to be able to define two of the variables and display the
solved variables with one Solve statement.

temp=Solve[convert,{power,voltage,current,r}];

temp/.{current -->2.82091,r -->377}//N
or
temp/.{voltage -->1063.48,r -->377}//N
or
temp/.{power -->30000,r -->377}//N

Thanks for any suggestions!

```

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