This is my current code and i'm not sure why it's not working. I am new to Mathematica, though.
FindInstance[{-11 "x1" - 20 "x2" - 9 "x3" + 8 "x4" - 9 "x5" -
14 "x6" - 9 "x7" - 11 "x8" + 3 "x9" == 1 &&
9 "x1" + 19 "x2" + 20 "x3" - 12 "x4" + 2 "x5" - 13 "x6" -
17 "x7" + 10 "x8" + 17 "x9" == -14 &&
15 "x1" + 2 "x2" + 17 "x3" + 15 "x4" - 20 "x5" - 10 "x6" - "x7" +
9 "x8" + 8 "x9" == -6 &&
13 "x1" + 13 "x2" - 8 "x3" + 5 "x4" - 8 "x5" - 12 "x6" + 11 "x7" -
19 "x8" + 11 "x9" == -17 &&
-18 "x1" - 5 "x2" - 18 "x3" - 7 "x4" - 2 "x5" - 20 "x6" + 2 "x7" - 5 "x8" -
17 "x9" == -1 &&
-3 "x1" - 7 "x2" + 2 "x3" + 5 "x4" - 9 "x5" - 8 "x6" - 4 "x7" + 18 "x8" - 9 "x9" == -18 &&
4 "x1" + 18 "x2" + 5 "x3" + 15 "x4" + 14 "x5" - 7 "x6" + 2 "x7" +
8 "x8" - 14 "x9" == 5 &&
-15 "x1" + "x2" - 16 "x3" - 16 "x4" + 3 "x5" - 5 "x6" -
10 "x7" + 7 "x8" + 16 "x9" == 5 &&
-5 "x1" + 7 "x2" + "x3" - 13 "x4" - 4 "x5" + 14 "x6" -
19 "x7" + "x8" - 14 "x9" == 8},
{x1, x2, x3, x4, x5, x6, x7, x8, x9}, Reals]
Here is the error that I am getting: FindInstance::exvar: The system contains a nonconstant expression x1 independent of variables {x1,x2,x3,x4,x5,x6,x7,x8,x9}.
Here are the equations on their own:
-11 x1-20 x2-9 x3+8 x4-9 x5-14 x6-9 x7-11 x8+3 x9==19
x1+19 x2+20 x3-12 x4+2 x5-13 x6-17 x7+10 x8+17 x9==-14
15 x1+2 x2+17 x3+15 x4-20 x5-10 x6-x7+9 x8+8 x9==-6
13 x1+13 x2-8 x3+5 x4-8 x5-12 x6+11 x7-19 x8+11 x9==-17
-18 x1-5 x2-18 x3-7 x4-2 x5-20 x6+2 x7-5 x8-17 x9==-1
-3 x1-7 x2+2 x3+5 x4-9 x5-8 x6-4 x7+18 x8-9 x9==-18
4 x1+18 x2+5 x3+15 x4+14 x5-7 x6+2 x7+8 x8-14 x9==5
-15 x1+x2-16 x3-16 x4+3 x5-5 x6-10 x7+7 x8+16 x9==5
-5 x1+7 x2+x3-13 x4-4 x5+14 x6-19 x7+x8-14 x9==8
I was experementing with the FindInstance function because I believe the Solve function can only do it for up to 4 variables, but again I could be wrong. What's the best way to do this? I'm on Mathematica 10 if that makes any difference.