HP Prime Graphing Calculator - Manual (Page 269)

Solve app 265
Solution information
When you are solving a single equation, the button
appears on the menu after you tap . Tapping
displays a message giving you some information about the
solutions found (if any). Tap
to clear the message.
Message Meaning
Zero The Solve app found a point where both
sides of the equation were equal, or where
the expression was zero (a root), within the
calculator's 12-digit accuracy.
Sign
Reversal Solve found two points where the two sides
of the equation have opposite signs, but it
cannot find a point in between where the
value is zero. Similarly, for an expression,
where the value of the expression has
different signs but is not precisely zero.
Either the two values are neighbors (they
differ by one in the twelfth digit) or the
equation is not real-valued between the two
points. Solve returns the point where the
value or difference is closer to zero. If the
equation or expression is continuously real,
this point is Solve’s best approximation of
an actual solution.
Extremum Solve found a point where the value of the
expression approximates a local minimum
(for positive values) or maximum (for
negative values). This point may or may not
be a solution.
Or:
Solve stopped searching at
9.99999999999E499, the largest number
the calculator can represent.
Note that the Extremum message indicates
that it is highly likely that there is no
solution. Use Numeric view to verify this
(and note that any values shown are
suspect).