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Question

Using cofactors of elements of third column, evaluate Δ=∣ ∣1xyz1yzx1zxy∣ ∣

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Solution

Given: Δ=∣ ∣1xyz1yzx1zxy∣ ∣
Minor of a13=M13=1y1z
M13=1×z1×y=zy
Minor of a23=M23=1x1z
M23=1×z1×x=zx
Minor of a33=M33=1x1y
M33=1×y1×x=yx
Cofactor of a13=A13=(1)1+3M13=(1)4.(zy)=zy
Cofactor of a23=A23=(1)2+3.M23=(1)5.(zx)=xz
Cofactor of a33=A33=(1)3+3.M33=(1)6.(yx)=yx
Now,
Δ=a13A13+a23A23+a33A33
Δ=yz(zy)+zx(xz)+xy(yx)
Δ=yz2y2z+zx2z2x+xy2x2y
Δ=(yz2y2z)+(xy2z2x)+(zx2x2y)
Δ=yz(zy)+x(y2z2)+x2(zy)
Δ=yz(yz)+x(y2z2)x2(yz)
Δ=yz(yz)+x(y+z)(yz)x2(yz)
Δ=(yz)(yz+x(y+z)x2)
Δ=(yz)(z(xy)x(xy))
Δ=(xy)(yz)(zx)
Therefore, the value of determinant is (xy)(yz)(zx)

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