(i) (2x + y – c)2 – (2x -p + c)2
= (2x + P – c + 2x – P + c)(2x + p – c – 2x + p – c)
= (4x)(2p – 2c)
= (4x)2(p – c) = 8x(p – c)
(ii) (x2 + y2 – z2)2 – (x2 – y2 + z2)2
= (x2 + y2 – 2 + x2 – y2 + z2)(x2 + y2 – z2 – x2 + y2 – z2)
= (2x2)(2y2 – 2z2)
= (2x2)2(y2 – z2)
= 4x2(y2 – z2)
(iii) (a + b + c)2 + (a – b + c)2 + (a + b – c)2
=a2 + b2 + c2 + 2ab + 2bc + 2ac + a2 + b2 + c2 – 2ab – 2bc + 2ac
+ a2 + b2 + c2 + 2ab – 2bc – 2ac
= 3 (a2 + b2 + c2) + 2ab – 2bc + 2ca
