hp40g+.book Page 21 Friday, December 9, 2005 1:03 AM
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.)
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
| 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 | To find the derivative of the function in HOME, use a |
in HOME | formal variable in place of X. If you use X, the |
Using mathematical functions |
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