# Deleting all zero columns.

by pondzo
Tags: columns, deleting
 P: 66 Yeah thats what i was wondering my self. how did this variable even get incorporated into the matrix if it doesn't affect it. its almost as if the variable doesn't exist, ghost variable? Any way the question was; $$\begin{pmatrix} 1 & 0 & 0 & 0 & 0 & | & 0\\ 0 & 0 & 6 & 3 & 1 & | & π\\ 0 & 0 & 0 & 4 & 3 & | & 7\\ 0 & 0 & 0 & 0 & k^2 - 1 & | &0 \end{pmatrix}$$ which statement is correct; A) The only values for k in which there are infinitely many solns are k=1 and k=-1 B) when k=1 or -1 there are no solutions C) There are always infinitely many solutions D) when k=1 or -1 there is a unique solution E) when k≠1 or -1 there are no solutions I thought it was between either A or C but i wasnt sure if an all zero column meant infinite solutions (in which case it would be C) or whether the all zero column could be excluded (in which case it would be A).