How Works; Entering Your Own Initial Guesses - HP -225 Owner's Manual

How Works
uses an iterative (repetitive) technique to solve for the un-
known. The technique starts by substituting two initial guesses for the
unknown into the equation. Based on its results with those guesses,
generates another, better guess. Through successive iterations,
finds a value that sets the left side of the equation equalto the
right side.
Some equations are more difficult to solve than others. In some cases,
you will have to enter initial guesses yourself in order to find the so-
lution (see "Entering Your Own Initial Guesses" below.) If is
unable to find a solution, it displays an error message.
See appendix B for additional information about [SOLVE].
Entering Your Own Initial Guesses
The two initial guesses that uses are:
B The number currently stored in the unknown.
B The last number that was in the display before you pressed
W(soLvE].
Since starts its search for the answer in the range between the
two guesses, entering your own guesses has the following advantages:
B Good guesses can reduce the time required to find a solution.
B If there is more than one solution, the guesses can help select the
desired answer. For example, the equation of motion in the library:
X=S+V+5XAXT"2
can have two solutions for T. You can calculate either answer by
entering appropriate guesses.
B If an equation does not allow certain values for the unknown,
guesses can help you avoid those values. For example, the
equation:
Y=T+LOG(X)>
does not allow values X < 0. Appropriate guesses can help
avoid the math errors LOG(8> and LOG(NEG).
6: Evaluating and Solving Equations 87