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CMinh rằng: Nếu x+y-2=0 thì giá trị các biểu thức sau là những hằng số: x^3+x^2y-2x^2-x^2y-xy^2+2xy+2y+2x-2
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$x^3 + x^2y – 2x^2 – x^2y – xy^2 + 2xy + 2y + 2x – 2 $
$= x^2(x + y) – 2x^2 – xy(x+y) + 2xy + 2(y+x) – 2$
$= 2x^2 – 2x^2 – 2xy + 2xy + 2.2 – 2$
$= 4-2 = 2$