toán nâng cao 8

L

luffy_1998

$x+y+z=0 \rightarrow x = - (y + z)$
$\rightarrow x^3+y^3+z^3 = - (y + z)^3 + y^3 + z^3 = - 3y^2z - 3yz^2 = -3yz(y + z) = 3xyz$
 
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