crawforddavid2006

How do you make a variable unknown in TI-83+ Basic?

chepfaust

you can "delvar <variable>" or just set it to 0; you don't have many options with basic. when a variable is delvar'ed it's still equal to 0; it just doesn't occupy any memory space.

crawforddavid2006

Sorry i should have specified. What i meant was in my program i want it to go to a different equation if the variable is unknown. How can i do that?

chepfaust

i'm pretty sure the only way you'll be able to do that is if you say "if <variable> = 0..." but that of course would cause problems if a known variable happens to equal 0.

so, as far as i know (and i used 83+ basic a LOT back in the day) there is no way to determine if a variable is unknown using basic.

if you were trying to make a program that would solve for a given variable in the equation like "x + y = z" ...

prompt x,y,z

have the user enter something conspicuous that a user would probably never actually type the entire length of like sin(69) or pi for the value of the unknown variable. then you can just check to see which variable equals sin(69) or pi and go from there. it's not the most intuitive and userfriendly solution, but it would get the job done.

crawforddavid2006

that did not work so i tried something else which helped here is an example

[begining of code]

Disp "UNKOWN=X"
Disp "ENTER A"
Input A
Disp "Enter B"
Input B
Disp "Enter C"
Input C
If C=X
√(A² + B²)→C
If B=X
√(C²-A²)→B
If A=X
√(C²-B²)→A
Disp “Answer Is”
Disp “A”
Disp A
Disp “B”
Disp B
Disp “C”
Disp C

crawforddavid2006

This is for one of my programs could you please help

i am trying to solve for “T” could u help?

P = Principal
R = Rate in decimal
N = Number of times compounded a year
T = Number of Year Compounded
A = Finishing Amount

A = P(1 + (R/N))NT

And after that could u help me solve for “N”

chepfaust

this program isn't going to work because x is a numerical value that is 0 by default. so if the user types in "x" for the variable they don't know, the calculator will interpret it as 0, and you'll have the problem i mentioned earlier. if another program you used stored a different value to x already, say, 14, your output is going to be seriously skewed because the calculator will interpret x as 14--NOT an unknown number.

if what i suggested didn't work, then you probably didn't implement it correctly. try this: replace all instances of "x" with pi. not just 3.14, i'm talking about the pi variable you get when you push 2nd ^. this way, in order to throw the program off the user would physically have to type 3.141592654 (assuming you're in float mode, where decimals don't get rounded).

so the first line would be disp "UNKNOWN=<pi character>" and your if statements would be if A=<pi character> then / if B=<pi character> then / etc.

chepfaust

ugh, math is NOT one of my strong points

you do know the 83/83+ has a built-in equation solver that is much more powerful than anything one can write in basic? if you can rearrange the variables to make the equation equal to 0, you can put the equation in the solver and let the calculator handle the rest. it will only solve for "x" but "x" is equivalent to "t" in your case.

furthermore, if you have the pc-to-calc link cable, i'm pretty sure either TI themselves or a third party at ticalc.org has released a full-blown equation solver that you can flash onto the calc. you might want to look into that.

i'm -seriously- retarded when it comes to figuring out anything more complex than simple addition and subtraction, so sorry i can't help you with this particular situation

crawforddavid2006

Thanks anyways
David

tempest

Umm...

A = P(1 + R)^(NT)

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