(x + y + x)3 = (y + 2 – x)3 + (2 + x – y)3 + (x + y – 2)3 + kxyz
we see that by putting x = 0, the expression vanishes.
so x is a factor of the expression similarly y,z are factors of that expression.
The given expression is of 3rd degree & the factors so far obtained are also of 3rd degree hence if there is any constant factors supposing it to be k.
Then in order to find k
put x = 1, y = 1, z = 1