Repeated use of the identity (x+y)(x−y)=x2−y2 leads to (5​+6​+7​)(5​+6​−7​)=(5​+6​)2−(7​)2=(11+230​)−7=4+230​, (5​−6​+7​)(−5​+6​+7​)=(7​)2−(5​−6​)2=7−(11−230​)=−4+230​ and (4+230​)(−4+230​)=(230​)2−42=120−16=104​.