@Min
Đáp án+Giải thích các bước giải:
a, (x + y)2 + (x – y)2
= x2 + 2xy + y2 + x2 – 2xy + y2
= 2x2 + 2y2
b, 2(x – y)(x + y) + (x + y)2 + (x – y)2
= [(x + y) + (x – y)]2 = (2x)2 = 4x2
c, (x – y + z)2 + (z – y)2 + 2(x – y + z)(y – z)
= (x – y + z)2 + 2(x – y + z)(y – z) + (y – z)2
= [(x – y + z) + (y – z)]2 = x2