Expand each of the following, using suitable identities:
(i) `(x+2y+4z)^2` (ii) `(2x-y+z)^2` (iii) `(-2x+3y+2z)^2`
(iv) `(3a-7b-c)^2`(v) `(-2x+5y-3z)^2` (vi) `[1/4a-1/2b+1]^2`