A+B=⎡⎢⎣15120−1−321⎤⎥⎦+⎡⎢⎣342−120253⎤⎥⎦
=⎡⎢⎣1+35+41+22−10+2−1+0−3+22+51+3⎤⎥⎦=⎡⎢⎣49312−1−174⎤⎥⎦
B−C=⎡⎢⎣342−120253⎤⎥⎦−⎡⎢⎣40113−2223⎤⎥⎦
=⎡⎢⎣3−44−02−1−1−12−30−(−2)2−25−23−3⎤⎥⎦=⎡⎢⎣−141−2−12030⎤⎥⎦
A+(B−C)=⎡⎢⎣15120−1−321⎤⎥⎦+⎡⎢⎣−141−2−12030⎤⎥⎦
=⎡⎢⎣1+(−1)5+41+12+(−2)0+(−1)−1+2−3+02+31+0⎤⎥⎦=⎡⎢⎣0920−11−351⎤⎥⎦
(A+B)−C=⎡⎢⎣49312−1−174⎤⎥⎦−⎡⎢⎣40113−2223⎤⎥⎦
=⎡⎢⎣4−49−03−11−12−3−1−(−2)−1−27−24−3⎤⎥⎦=⎡⎢⎣0920−11−351⎤⎥⎦
Hence, we have verified that A+(B−C)=(A+B)−C.