Question

Use matrices to solve
x+ +2y+3z=7
-x+2y-z
-x+y-2z=-2
I've tried many way cant figure out

Answer 1

one way:
Ax=B, so you want A^-1 so that

x = A^-1 B

A =
(1 2 3)
(-1 2 -1)
(-1 1 -2)
B =
(7)
(?)
(-2)

A^-1 = 1/2 *
(3 -7 8)
(1 -1 2)
(-1 3 -4)

Now if you supply the missing value in B, you can do the multiply and get (x y z), the solution.

Or, you can do row operations as in Gaussian elimination. There's a handy calculator at

http://www.gregthatcher.com/Mathematics/GaussJordan.aspx