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kagaminex

ta có: a=-b-c
b=-a-c
c=-a-b

$a^3+b^3+c^3=(a+b)(a^2-ab+b^2)+c^3$

$=-c(a^2-ab+b^2-c^2)$

$=-c[(a-c)(a+c)-b(a-b)]$

$=-c[-b(a-c+a-b)]$

$=bc(2a-b-c)$

$=3abc(đccm)$
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