HP 39gII User Manual page 156

Not enough data
146
If you are using the
general input form, you
need to specify at least
three values for the
Triangle Solver to be able
to calculate the remaining
attributes of the triangle. If
you specify less than three, Not enough data appears
on the screen.
If you are using the simplified input form (for a right-
angled triangle), you must specify at least two values.
In addition, you cannot specify only angles and no
lengths.
Triangle Solver app