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Using mathematical functions 13-21
names. The HP 40gs has six formal names available for
use in symbolic calculations. These are S1 to S5. When
you perform a calculation that contains a formal name,
the HP 40gs does not carry out any substitutions.
You can mix formal names and real variables. Evaluating
(A+B+S1)
2
will evaluate A+B, but not S1.
If you need to evaluate an expression that contains formal
names numerically, you use the | (where) command,
listed in the Math menu under the Symbolic category.
For example to evaluate (S1*S2)
2
when
S1=2 and
S2=4, you would enter the calculation as follows:
(The | symbol is in the CHARS menu: press
CHARS.
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 13-22 for an example.
Finding derivatives
The HP 40gs can perform symbolic differentiation on
some functions. There are two ways of using the HP 40gs
to find derivatives.
• You can perform differentiations in HOME by using
the formal variables, S1 to S5.
• You can perform differentiations of functions of X in
the Function aplet.
To find derivatives
in HOME
To find the derivative of the function in HOME, use a
formal variable in place of X. If you use X, the
hp40g+.book Page 21 Friday, December 9, 2005 1:03 AM