Cách làm cho bạn:
A = x2 – 2y + 4xy + y2
B = - 4x2 – 2x – 4xy – y2 + 1
A + B = (x2 – 2y + 4xy + y2) + (- 4x2 – 2x – 4xy – y2 + 1)
= x2 – 2y + 4xy + y2 - 4x2 – 2x – 4xy – y2 + 1
= (x2 - 4x2) + (4xy– 4xy) + (y2 – y2) – 2y – 2x + 1
= -3x2 – 2y – 2x + 1
A – B = (x2 – 2y + 4xy + y2) - (- 4x2 – 2x – 4xy – y2 + 1)
= x2 – 2y + 4xy + y2 + 4x2 + 2x + 4xy + y2 - 1
= (x2 + 4x2) + (4xy+ 4xy) + (y2 + y2) – 2y + 2x - 1
= 5x2 +8xy + 2y2 – 2y – 2x + 1
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