# Math Help - matrices with the ti89

1. ## matrices with the ti89

ok im trying to do a matrix, or get the determinant from a matrix, but every time i enter it, i get this data type error? can someone tell me why?

first off im doing a variation of parameter problem and i need to find the eigenvalues of this 2x2 matrix.

where lambda should be im inserting an x, i figure once i get the result i could solve for x and then get my lamba values.

the matrix is 3 -5
3/4 -1

can someone show me how to enter this into my calc without getting the error messages.

2. Originally Posted by slapmaxwell1
ok im trying to do a matrix, or get the determinant from a matrix, but every time i enter it, i get this data type error? can someone tell me why?

first off im doing a variation of parameter problem and i need to find the eigenvalues of this 2x2 matrix.

where lambda should be im inserting an x, i figure once i get the result i could solve for x and then get my lamba values.

the matrix is 3 -5
3/4 -1

can someone show me how to enter this into my calc without getting the error messages.

On the 89, the general input for a matrix is:

Code:
[a,b,c;d,e,f;g,h,i]
where the semicolons are used to end a row, and this would return

$\begin{bmatrix}a & b & c\\ d & e & f\\ g & h & i\end{bmatrix}$

on your calculator screen. If you want to compute the determinant, then you should use

Code:
det([a,b,c;d,e,f;g,h,i])
and so on for other types of operations.

So for your example, to find the eigenvalues, you could do it all in one input:

Code:
csolve(det([3-x,-5;3/4,-1-x]) = 0,x)
I put csolve just in case the eigenvalues are complex.

I hope this helps!

P.S. You need to make sure that nothing is stored in the variable you're using! Otherwise you'll get an error!! The easiest way to fix that would be to use DelVar "list of variable(s)"

3. thanks alot for that, by the way what is this cssolve command, i never heard of it before.

4. Originally Posted by slapmaxwell1
thanks alot for that, by the way what is this cssolve command, i never heard of it before.
csolve stands for complex solve; i.e. it will return any complex solutions the equation may have. For instance, csolve(x^2+1=0,x) returns x=i or x=-i. However, if you use the regular solve, solve(x^2+1=0,x) returns false, meaning that its not possible to solve for x^2+1 in the real numbers.