8x³+4x²-2x-1
=(8x³+4x²)-(2x+1)
=4x²(2x+1)-(2x+1)
=(2x+1)(4x²-1)
=(2x+1)[(2x)²-1]
=(2x+1)(2x+1)(2x-1)
=(2x-1)(2x+1)²