HP 35s Scientific Calculator - Manual (Page 330)

D-8 More about Solving
Now, solve to find the root.
When SOLVE Cannot Find a Root
Sometimes SOLVE fails to find a root. The following conditions cause the message
  :
The search terminates near a local minimum or maximum (see figure a,
below).
The search halts because SOLVE is working on a horizontal asymptote—an
area where f(x) is essentially constant for a wide range of x (see figure b,
below).
The search is concentrated in a local "flat" region of the function (see figure c,
below).
In these cases, the values in the stack will be same as the values before executing
SOLVE.
 
 Checksum and length.

Cancels Equation mode.
Keys: Display: Description:

X
 _
Your initial guesses for the root.


Selects Equation mode; displays
the equation.
X
  
No root found for f(x).