(2x+1)×(2x+1)×(2x+1)×(2x+1) =

(2x + 1)⁴
= (2x + 1) × (2x + 1) × (2x + 1) × (2x + 1)
= (2x × 2x × 2x × 2x) (1 × 1 × 1 × 1)
= 16x⁴ + 1