`b)`
`(4x+1)(12x-1)(3x+2)(x+1) - 4`
` = [ (4x+1)(3x+2)] . [ (12x-1)(x+1)] - 4`
` = (12x^2 + 8x + 3x + 2)(12x^2 + 12x - x - 1) - 4`
`= (12x^2 + 11x + 2)(12x^2 + 11x-1) - 4`
` = [ (12x^2 + 11x + 0,5) + 1,5] [ (12x^2 + 11x + 0,5) - 1,5] - 4`
` = (12x^2 + 11x + 0,5)^2 - (1,5)^2 - 4`
` = (12x^2 +11x + 0,5)^2 - 25/4`
` = (12x^2 +11x+0,5)^2 - (5/2)^2`
` = (12x^2 + 11x + 0,5 - 5/2)(12x^2 + 11x + 0,5 + 5/2)`
` = (12x^2 + 11x-2)(12x^2 + 11x +3)`
