If A=⎡⎢⎣102021203⎤⎥⎦, prove that A3−6A2+7A+2I=0.
A2=A×A=⎡⎢⎣102021203⎤⎥⎦⎡⎢⎣102021203⎤⎥⎦=⎡⎢⎣1+0+40+0+02+0+60+0+20+4+00+2+32+0+60+0+04+0+9⎤⎥⎦=⎡⎢⎣5082458013⎤⎥⎦A3=A2×A=⎡⎢⎣5082458013⎤⎥⎦⎡⎢⎣102021203⎤⎥⎦
=⎡⎢⎣5+0+160+0+010+0+242+0+100+8+04+4+158+0+260+0+016+0+39⎤⎥⎦=⎡⎢⎣210341282334055⎤⎥⎦∴A3−6A2+7A+2I=⎡⎢⎣210341282334055⎤⎥⎦−6⎡⎢⎣5082458013⎤⎥⎦+7⎡⎢⎣102021203⎤⎥⎦+2⎡⎢⎣100010001⎤⎥⎦
=⎡⎢⎣210341282334055⎤⎥⎦−⎡⎢⎣3004812243048078⎤⎥⎦+⎡⎢⎣7014014714021⎤⎥⎦+⎡⎢⎣200020002⎤⎥⎦=⎡⎢⎣21−30+7+20−0+0+034−48+14+012−12+0+08−24+14+223−30+7+034−48+14+00−0+0+055−78+21+2⎤⎥⎦=⎡⎢⎣000000000⎤⎥⎦=0
Hence proved.