1. ## [TI-83] Solve Quadratic Equations

Simple program for the Texas Instruments TI-83 graphics calculator, for solving quadratic equations.

Code:
```QUADEQ

a+bi
Disp "INSERT A,B,C"
Prompt A,B,C
(-B+(√(Bē-4AC)))/(2A)->V
(-B-(√(Bē-4AC)))/(2A)->W
If (Bē-4AC)<0
Then
Fix 6
Else
Float
End
Disp "ZEROS:"
If Str0="Y"
Then
Disp V>Frac,W>Frac
Else
Disp V>Dec,W>Dec
End
((-B)/(2A))->D
If A<0
Then
Disp "LOCAL MAX="
Else
Disp "LOCAL MIN="
End
If Str0="Y"
Then
Disp E>Frac,"WHEN X=",D>Frac
Else
Disp E>Dec,"WHEN X=",D>Dec
End
Float```
And an accompanying function to turn fractions mode on and off:
Code:
```SETMODE

Lbl A
"Y"->Str0
Disp "FRACTIONS ON"
Stop
Lbl B
"N"->Str0
Disp "FRACTIONS OFF"```

3. ## Re: [TI-83] Solve Quadratic Equations

When I try to run the program, I'm getting this error message:
ERR: UNDEFINED
and when I choose Goto, it takes me back to this line:
If Str0="Y"

I don't understand what I've done wrong.

4. ## Re: [TI-83] Solve Quadratic Equations

I'm sorry, I didn't make it clear in the original post. You need to run the SETMODE program first in order to assign Str0; then run QUADEQ.

One probably ought to build in a check for this condition in QUADEQ. Perhaps an exercise for you?

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