HP 48G - Manual (Page 58)

S t e p 1 :
You’re already working with
R A T F U N C ,
and the x variable
field is highlighted, so you are ready to enter the guess.
2 f ^ f e n t e r ! ^^»SDLVE ECiUflTIDN^^*
ENTER FUNCTIBH TD_;niVE__________
S t e p 2 : Solve for x again and examine the new solution,
( T ) S O L V E I N F O
SOLVE EQUATION
EQ:
I
3.00000000001
Sign Reversal
ENTER VALUE DR PRESS SOLVE
imM
S t e p 3 :
Press OK to remove the message box.
Interpreting the Results
The S i g n Reoers-al message means that the solver has found two
adjacent sample points at which the value of the expression is opposite
in sign, but hasn’t found one sample point that makes the expression
zero (to 12 digits). This can happen at a legitimate solution—the
finite numerical precision making it impossible for the HP 48 to find
the actual zero. But it can also occur at a discontinuity, where the
graph of the equation “jumps” across the x-axis without ever touching
it.
Two kinds of Sign Reversais
VJ
Discontinuity
5-4 Solving Equations