Given A=[3−112]
Calculate A2:
A2=A×A
=[3−112]×[3−112]
=[(3)(3)+(1)(−1)(−1)(3)+(2)(−1)(3)(1)+(1)(2)(−1)(1)+(2)(2)]
=[9−1−3−23+2−1+4]
=[8−553]
Calculate 5A:
5A=5×[3−112]
=[15−5510]
Calculate A2−5A:
A2−5A=[8−553]−[15−5510]
=[8−15−5−(−5)5−53−10]
=[−700−7]
The identity matrix I=[1001]
Therefore:
[−700−7]=−7×[1001]=−7I
The answer is −7I.