So matrix A is
1 2 1 0
3 1 2 3
2 5 0 1
2 -1 1 3
how will i go able showing that this matrix ISNT invertible?
You double posted, you should probably edit one and say it was an accident or someone might get mad at you.
There's lots of ways,
Row reduce to find a zero row,
Find that the det = 0
and a whole bunch of over equivalent statements,
Google singular matrix and go to the wiki