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# Matrix equations with given, find algorithm

## Matrix equations with given, find algorithm

(OP)
Hi,

I've been trying to solve this equation for a FEM algorithm with 2 triangular elements (first element has nodes 1,2,3 and the second element has 1,3,4) but Mathcad just shows "This variable is undefined". The equation is in form of V=S^(-1)*F, where V:{V1,V2,V3,V4} and symbolizes electric potential. Now, I want to "inject" a potential of 10 V in the point 4. I don't know how to approach this error because I cannot simply delete the last row (overdetermined system error)

I would appreciate some ideas :)
Thanks!

For a better understanding of the situation please find attached the mathcad file.
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