LetmidpointofdiagonalsbeM.thenco−ordinateofMwillbeauniquevalueusingAandC,co−ordinatesofmid−pointsofdiagonalsare((3+12),(3+72),(3+72))=M(2,5,5)nowusingBandD,co−ordinatesofmid−pointsshouldbeM((x+02),(y+62),(z+32))bycomparing,weget(x2)=2orx=4(y+62)=5ory=10−6=4(z+32)=5orz=10−3=7∴M(4,4,7)