7 Using the Solver
Unfortunately the HP-42S does not have an equation editor like that of the 33S. To use the solver and
numeric integration we must enter the equation in a program which must have a global name.
Let's suppose we want to solve the equation x
2
– 5x + 4 = 0 . We are going to enter it in a program.
For example:
01 LBL “FX” (“FX” is the global name of the program)
02 MVAR “X” (You find this in Solver menu. I will explain this later)
03 RCL “X”
04 X↑2
05 5
06 RCL “X”
07 ×
08 –
09 4
10 +
11 END
Well, as you can see we don't enter the equation f(x)=0 but just the function f(x). The MVAR function
tells the calculator what variables must appear in the solver menu. We suppose all variables are in the
memory so we use the RCL function.
Now we leave the program mode and we go to the Solver menu. What should appear is
Select Solve Program
followed by a menu of available Solver programs. Then in our case we select FX and we give a start
value, for example 8 and we press X to enter this value. Again we press X to calculate the correct
value of x which gives us X=4.
But this equation does not have only one solution. X=1 is also a solution. To get it we can enter 2 for
example for the start value.
If you want to solve numerically many equations of the form ax
2
+ bx + c = 0 you can write a program
such as
01 LBL “FX”
02 MVAR “A”
03 MVAR “B”
04 MVAR “C”
05 MVAR “X”
06 RCL “X”
07 X↑2
08 RCL “A”
09 ×
10 RCL “B”
11 RCL “X”
12 ×
13 +
14 RCL “C'
15 +
16 END
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