HP 39gII User Manual page 151

Solve a two-by-
two system
NOTE
Linear Solver app
If the three-equation input
form is displayed and you
want to solve a two-
equation set, press
.
You can enter any expression that resolves to a numerical
result, including variables; you can enter the name of a
stored variable. For more information on storing
variables, see the chapter titled Using mathematical
functions.
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