The following matrix can be converted to a Identity matrix using elementary row transformations ⎡⎢⎣122255−111⎤⎥⎦
False
R1→R1+R3 ⎡⎢⎣1−12+12+1255−111⎤⎥⎦
⎡⎢⎣033255−111⎤⎥⎦
R2→R2−2R3 ⎡⎢⎣0332−25+25+2−111⎤⎥⎦
⎡⎢⎣033077−111⎤⎥⎦
R1→R2−3/7R2 ⎡⎢ ⎢⎣03−37(7)3−37(7)177−111⎤⎥ ⎥⎦
⎡⎢⎣000077−111⎤⎥⎦
R2→R2/7 ⎡⎢⎣000011−111⎤⎥⎦
R3→R3−R2 ⎡⎢⎣000011−100⎤⎥⎦
R3→(−1)R3andR1↔R3
⎡⎢⎣100011000⎤⎥⎦
Now irrespective of what we do we cannot make it a identity matrix. Without disturbing other elements. A more detailed explanation can be understood using rank which we will see ahead.