I must be doing something silly...

[DanJoffe]

I'm getting a "this variable is undefined". I don't know why...It's Mathcad 15..probably something simple I'm overlooking, but I don't see it!

Hope someone can point it out, and I will happily say "D'Oh!"

[DanJoffe]

It's funny...I just cut and pasted this to a new file, and it solves it with no complaints!...oh well..

[HarveyHensley]

You have an extra "Given" statement at the top of the file. Removing it allowed program to run.

[DanJoffe]

D'Oh!

Thanks!

[Werner_E · Accepted solution]

You have written "Given" twice. Delete one og them, preferably the first, and you get a solution.

Find attached a version without the need for copy and paste.

[Werner_E]

Forgot to attach the file and have deleted it.

Anyway here is a fully numerical approach.

It seems that with the values you provided at the end of your first sheet there is no solution where all three resistors woul have positive values. Anything wrong with the equations??

See attachment

EDIT: Found the symbolic solution I mentioned and compared its results to the numerics. See new attachment.