`a) (x+1)^3 + (x-2)^3`
` = [ (x+1) + (x-2) ] . [ (x+1)^2 - (x+1).(x-2) + (x-2)^2]`
` = (x+1+x-2) . [ (x^2 +2x+1) - (x^2 - 2x + x -2) + (x^2 - 4x+4)]`
` = (2x - 1) . (x^2 + 2x + 1 - x^2 + 2x - x + 2 + x^2 - 4x + 4)`
` = (2x-1) . (x^2 -x+7)`
`b) 1 - y^3 + 6xy^2 - 12x^2y + 8x^3`
` = 1 - (y^3 - 6xy^2 + 12x^2y - 8x^3)`
` = 1 - ( y - 2x)^3`
` = [ (1 - ( y-2x)] . [ 1 + y - 2x + (2x-y)^2]`
` = (1 - y + 2x) . (1 + y - 2x + y^2 - 4xy + 4x^2)`
`c) 2004^2 - 16`
` = 2004^2 - 4^2`
` =(2004 - 4) . (2004+ 4)`
` = 2000 . 2008`
