L.H.S =∣∣
∣∣xCrxCr+1xCr+2yCryCr+1yCr+2zCrzCr+1zCr+2∣∣
∣∣
Applying C2→C2+C1 and C3→C3+C2
∣∣
∣∣xCrxCr+1+xCrxCr+2+xCr+1yCryCr+1+yCryCr+2+yCr+1zCrzCr+1+zCrzCr+2+zCr+1∣∣
∣∣
∣∣
∣
∣∣xCrx+1Cr+1x+1Cr+2yCry+1Cr+1y+1Cr+2zCrz+1Cr+1z+1Cr+2∣∣
∣
∣∣ (By Pascal
triangle rub i.e., nCr+nCr−1=n+1Cr)
Applying C3→C3+C2
=∣∣
∣
∣∣xCrx+1Cr+1x+1Cr+1+x+1Cr+2yCry+1Cr+1y+1Cr+1+y+1Cr+2zCrz+1Cr+1z+1Cr+1+z+1Cr+2∣∣
∣
∣∣
=∣∣
∣
∣∣xCrx+1Cr+1x+2Cr+2yCry+1Cr+1y+2Cr+2zCrz+1Cr+1z+2Cr+2∣∣
∣
∣∣