use the binomial theorem to expand (2x+1)^3
(2x + 1)³(2x + 1)(2x + 1)(2x + 1)(4x² + 2x + 2x + 1)(2x + 1)(4x² + 4x + 1)(2x + 1)(8x³ + 4x² + 8x² + 4x + 2x + 1)8x³ + 12x² + 6x + 1