7-10 Solve aplet
Using variables in equations
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).
Home variables 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.
HINT
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 
CLEAR to reset all 
values to zero in the Solve aplet’s Numeric view if you 
wish.)
Aplet variables 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
2
+10, you can enter F1(X)=50 in 
the Solve aplet to solve the equation X
2
+10=50.
HP 39gs English.book  Page 10  Wednesday, December 7, 2005  11:24 PM