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7 Using the Solver
Unfortunately the HP-42S does not have an equation editor like the 33S one. 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
− 5 x4=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 x
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 RCL function.
Now we leave the program mode and we go to the Solver menu. What should appear is
Select Solve Program
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 give to 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
a x
2
bxc=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 x
10 RCL “B”
11 RCL “X”
12 x
13 +
14 RCL “C'