# Using Variables In Equations - HP 40gs User Manual

Graphing calculator.

## Using variables in equations

Home variables
H I N T
Aplet variables
7-10
You can use any of the real variable names, A to Z and
θ. Do not use variable names defined for other types,
such as M1 (a matrix variable).
All home variables (other than those for aplet settings, like
Xmin and Ytick) are global, which means they are
shared throughout the different aplets of the calculator. A
value that is assigned to a home variable anywhere
remains with that variable wherever its name is used.
Therefore, if you have defined a value for T (as in the
above example) in another aplet or even another Solve
equation, that value shows up in the Numeric view for this
Solve equation. When you then redefine the value for T
in this Solve equation, that value is applied to T in all
other contexts (until it is changed again).
This sharing allows you to work on the same problem in
different places (such as HOME and the Solve aplet)
without having to update the value whenever it is
recalculated.
As the Solve aplet uses existing variable values, be sure
to check for existing variable values that may affect the
solve process. (You can use
values to zero in the Solve aplet's Numeric view if you
wish.)
Functions defined in other aplets can also be referenced
in the Solve aplet. For example, if, in the Function aplet,
you define F1(X)=X
the Solve aplet to solve the equation X
CLEAR
2
+10, you can enter F1(X)=50 in
2
to reset all
+10=50.
Solve aplet