You cannot use equations from the 35s equation list in your own programs. But solving a 2x2 system is so trivial that it can be done in a very short user routine:
RCL A
RCL* F
RCL D
RCL* C

RCL A
RCL* E
RCL B
RCL* D

/
ENTER
RCL* B
+/
RCL+ C
RCL/ A
This returns the two unknowns in X and Y.
Actually you can also do this in just two lines, using the EQNfeature:
([A,D]*[F,C])/([A,B]*[E,D]>G)
([C,B]*[E,F])/G
Type "STO G" to enter ">G". Please also note that the minuses are unary (signs, not operators). This solution also works for A=0. ;)
Dieter
Edited: 17 Oct 2012, 3:28 p.m.