HP 39g Graphing Calculator - Manual (Page 160)

Symbolic calculations
The HP 39G/40G has the ability to perform symbolic
calculations, for example, symbolic integration and
differentiation. You can perform symbolic calculations in
HOME and in the Function aplet.
In HOME
Using formal
variables
When you perform calculations that contain normal variables,
the calculator substitutes values for any variables. For
example, if you enter A+B on the command line and press
I ENTER I, the calculator retrieves the values for A and B from
memory and substitutes them in the calculation.
To perform symbolic calculations, for example symbolic
differentiations and integrations, you need to use formal
names. The HP 39G/40G has six formal names available for
use in symbolic calculations. These are SO to S5. When you
perform a calculation that contains a formal name, the
HP 39G/40G does not carry out any substitutions.
You can mix formal names and real variables. Evaluating
(A+B+Sl) ^ will evaluate A+B, but not SI.
If you need to evaluate an expression that contains formal
names numerically, you use the I (where) command, listed in
the Math menu under the Symbolic category.
For example to evaluate (S1*S2 ) ^ when S l = 2 and
S2 = 4, you would enter the calculation as follows:
aICS1=2,S2=4>
64
B103I
(The I symbol is in the CHARS menu: press [ shift
The = sign is listed in the MATH menu under Symbolic
functions.)
Symbolic
calculations in
the Function
aplet
You can perform symbolic operations in the Function aplet’s
Symbolic view. For example, to find the derivative of a
function in the Function aplet’s Symbolic view, you define
two functions and define the second function as a derivative
of the first function. You then evaluate the second function.
See “To find derivatives in the Function aplet’s Symbolic
view’’ on page 10-24 for an example.
10-22 Using mathematical functions