Given:
∣∣ ∣∣x+42x2x2xx+42x2x2xx+4∣∣ ∣∣
Use operation: R1=R1+R2+R3
∣∣ ∣∣5x+45x+45x+42xx+42x2x2xx+4∣∣ ∣∣
Take common 5x+4.
(5x+4)∣∣ ∣∣1112xx+42x2x2xx+4∣∣ ∣∣
Use operation: R2=R2−R3
(5x+4)∣∣ ∣∣11104−xx−42x2xx+4∣∣ ∣∣
Take determinant with respect to first column.
=1(16−x2−2x2+8x)−2x(4−x−x+4)
=1(16−3x2+8x)−2x(8−2x)
=16−3x2+8x−16x+4x2
=16−8x+x2
=(4−x)2
Thus, ∣∣ ∣∣x+42x2x2xx+42x2x2xx+4∣∣ ∣∣=(5x+4)(4−x)2