Bài 3:
* A + B = x2 - 2x - y + 3y - 1 - 2x2 + 3y2 - 5x + y + 3
A + B = −x2 + 3y2 − 7x + 3y + 2
* A - B = x2 - 2x - y + 3y - 1 + 2x2 - 3y2 + 5x - y - 3
A - B = 3x2 − 3y2 + 3x + y − 4
Bài 4:
a, M + (5x2 - 2xy) = 6x2 + 9xy - y2
M = 6x2 + 9xy - y2 - 5x2 + 2xy
M = x2 − y2 + 11xy
b, (3xy - 4y2) - N = x2 - 7xy + 8y2
N = 3xy - 4y2 - x2 + 7xy - 8y2
N = −x2 + 10xy − 12y2
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