HP HP-32S - Choosing Initial Guesses for SOLVE

Choosing Initial Guesses for SOLVE
The two initial guesses come from:
• The number currently stored in the unknown variable.
H The number in the X-register (the display).
These sources are used for guesses whether you enter guesses or not. If
you enter only one guess and store it into the variable, then the sec
ond guess will be the same value since the display also holds the
number you just stored into the variable. Entering your own guesses
has these advantages:
• By narrowing the range of the search, guesses can reduce the time
required to find a solution.
• If there is more than one mathematical solution, the guesses can
direct the SOLVE procedure to the desired answer or range of an
swers. For example, the equation of motion
d = d0 + v0t + Vigt2
can have two solutions for t. You can direct the answer to the only
meaningful one (t > 0) by entering appropriate guesses.*
• If an equation does not allow certain values for the unknown,
guesses can prevent these values from occurring. For example, the
equation
y =.t + log*
results in an error if x < 0 (LOG<0), L0G<NEG>).
The example in the previous section('Finding the Roots of an Equa
tion*) used guesses to find three solutions to one equation. Here is
another example that examines the dimensions of a box (as does the
example on page 113) but with more restrictions.
*The example usingthis equation on page 116did not need to enter guesses before solving
for I because in the first part of the example we stored a value for T and solved for D. The
value thatwasleft in T wasa good (realistic) one, andit wasusedasa guess when solving
for T.
120 7: Solving ffor an Unknown Variable in an Equation