HP -28S Quick Reference
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HP-28S
LOGS Menu
General All of the following functions operate on real as well as complex numbers but
not on matrices or vectors.
LOG Logarithm base 10.
ALOG 10^x.
LN Logarithm base e.
EXP e^x.
LNP1 Returns ln(1+x) which is useful when x is close to 0.
EXPM Returns exp(x)-1 which is useful when x is close to 0.
SINH Hyperbolic sine.
ASINH Inverse hyperbolic sine.
COSH Hyperbolic cosine.
ACOSH Inverse hyperbolic cosine.
TANH Hyperbolic tangent.
ATANH Inverse hyperbolic tangent.
SOLV Menu
General The commands in this menu allow to find solutions for user-defined
functions. A solution is the value x where f(x)=0. This is also called a root
of the function.
• Note that only real but not complex roots can be found!
• SOLVR is the interactive version of the solver.
This mode can be invoked by a program. It offers a versatile user
menu for finding iterative solutions for (usually complicated)
functions. The "user interface" is the same as for example on the
HP-12C when solving for n, i, PM, PV, PMT and FV.
• ROOT is a non-interactive version which is mainly used in programs.
• Furthermore, ISOL can isolate (unique) variables from equations and
QUAD can calculate symbolic solutions for functions.
• A very powerful tool is the combination of the interactive plot
command DRAW (see PLOT Menu) and the solver: Visually
interesting points in the plot (ie. approximate roots) can be digitized
and passed as initial guesses to the solver.
Finding a
numerical
root
Follow these steps to interactively find a numerical root:
1. Store the function to be solved using STEQ, see below.
2. Press SOLVR to display a menu that shows all the variables used
inside the function.
3. Store the desired values in these variables. Also store an initial guess
in the variable that you want to solve for.
4. Press SHIFT and the menu button for the variable you want to solve
for. This will invoke the root finding process.
STEQ This stores the function that is to be solved in the global variable called
EQ. The function can be:
• An expression, ie. '3-x^2'.
In this case the solver finds the value for x where the expression is 0.
• An equation, ie. 'y=3*x^3 – 2*x'.
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