LHS =∣∣
∣
∣∣x2+1xyxzxyy2+1yzxzyzz2+1∣∣
∣
∣∣
Taking out common factors x,y and zf from R1,R2,R3 respectively, we get
=xyz∣∣
∣
∣
∣∣x+1xyzxy+1yzxyz+1z∣∣
∣
∣
∣∣
Applying R2→R2−R1
R3→R3−R1
=xyz∣∣
∣
∣
∣∣x+1xyz−1x1y0−1x01z∣∣
∣
∣
∣∣
Applying C1→xC1
C2→yC2
C3→zC3
=xyz×1xyz∣∣
∣∣x2+1y2z2−110−101∣∣
∣∣
=∣∣
∣∣x2+1y2z2−110−101∣∣
∣∣
Expanding along R3, we have
LHS =−1∣∣∣y2z210∣∣∣+1∣∣∣x2+1y2−11∣∣∣
=−1(−z2)+(x2+1+y2)=1+x2+y2+z2= RHS
Hence proved.