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 Các hằng đẳng thức thường gặp: 

$$(a+b+c)^2=a^2+b^2+c^2+2(ab+bc+ca)$$
$$(a+b+c)^3=a^3+b^3+c^3+3(a+b)(b+c)(c+a)$$
$$(a+b+c)(ab+bc+ca)=(a+b)(b+c)(c+a)+abc$$ Read the rest of this entry »

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