HP 39g+ Graphing manual Symbolic calculations, Sec, Using formal variables, SECvalue

SEC	Secant: 1/cosx.
	SEC(value)

Symbolic calculations

The hp 39g+ 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	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	, the calculator retrieves the values

for A and B from memory and substitutes them in the calculation.

Using formal variables

To perform symbolic calculations, for example symbolic differentiations and integrations, you need to use formal names. The hp 39g+ has six formal names available for use in symbolic calculations. These are S0 to S5. When you perform a calculation that contains a formal name, the hp 39g+ 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.)

11-20 Using mathematical functions