b) (x – y – z)^2 – (x – y)^2 + 2(x − y)z.
b) (x – y – z)2 – (x – y)2 + 2(x − y)z.
b) (x – y – z)2 – (x – y)2 + 2(x − y)z
= [(x – y) – z]2 – (x – y)2 + 2(x − y)z
= (x – y)2 – 2(x – y)z + z2 – (x – y)2 + 2(x – y)z
= [(x – y)2 – (x – y)2] + [–2(x − y)z + 2(x − y)z] + z2
= z2.