Solving Imaginary Numbers with TI89 Calculator

[Euphoriet]

Well I know it can solve for real numbers of X^n+x^(n-1)+ etc etc = 0

But was wondering if it could also solve when there are imaginary numbers involved?...

Thanks

 

[Justin Lazear]

Take a gander at the complex algebra functions.

f2(algebra) / A: Complex

One of them is cSolve().

--J

 

[Euphoriet]

Thanks that helps a lot, I remember reading this in the manual a long time ago...

hmm i take it inequalities would be a whole diff story.. I'm not even sure how to plug them in and thus not even graph them... let alone solve them. If you guys know about this.. it would be great if someone could clear it up.

Thanks

 

[Justin Lazear]

I'm not quite sure what you're trying to do, but the 89 can also handle inequalities.

Graphing them is not particularly easy, but you can convince the 89 to produce the standard shaded below/above the line graphs. It's really not worth the effort, though. May as well do it by hand.

The 89 can solve inequalities and handle inequalities a few different ways. You can place constraints on variables for pretty much anything you're doing, i.e.

Solve(x^2 - 2 = 0, x) | x > 0

will return $x = \sqrt{2}$

and Solve(x^2 - 2 = 0, x) | x < 0

will return $x = - \sqrt{2}$.

Note that the "| x > 0" part is the constraint.

The constraint expressions can do other neat things, too.

Alternatively,

Solve( x + 2 > 5, x)

returns

x > 3

as expected.

You run into some trouble when you're trying to solve systems of inequalities, though.

There are some other things you can do, particularly programming in the inequalities in the form of functions, but it can get pretty complicated.

What exactly are you trying to do?

--J

 

[Alkatran]

Also, make sure your "complexe format" (one of the Mode options) is not set to "Real"

 

[Euphoriet]

I'm just trying to figure out what my ti89 can and what can't do.

This is just something I want to know to save time:

Also.. let's say I have more then one variable in the equation



3x+7y

how can i tell it that x= 3 and y = 8?... I know you use |x=3 but I am not sure how to get y=8 in there also .. is this possible or do you have to do it in steps...

steps would mean

entering 3x+7y|x=3
letting the calc solve that
and then entering what it gives back
9+7y|y=8

 

[Alkatran]

You can assign values to variables permanently (can be deleted in another place) with one of the buttons near the bottom left (I believe it is an arrow...)

I think you can also use y1(0), which would reference the formula for your graph (set it to a constant and voila)

 

[Euphoriet]

hmm yeah I learned about permanent variables too.. But i was looking for seomtjhing like..

x3+7y|x=1, y = 4

and let the calc plug in both values accordingly

 

[Justin Lazear]

You have to use the "and" operator.

2nd-Math / Logic / and, if my memory's correct. Or you can just type it.

An example:

x^2 + 3y | x = -3 and y = 2

will return

15.

--J

 

[Euphoriet]

thanks... any other general tips and tricks would be appriciated.