Bài số kiểm tra giữa kì

T

transformers123

$\dfrac{a^3 + b^3}{a^3 +c^3}$

$=\dfrac{(a+b)(a^2-ab+b^2)}{(a+c)(a^2-ac+c^2)}$

$=\dfrac{(a+b)[(b+c)^2-b(b+c)+b^2]}{(a+c)[(b+c)^2-(b+c)c+c^2}$

$=\dfrac{(a+b)(b^2+2bc+c^2-b^2-bc+b^2)}{(a+c)(b^2+2bc+c^2-bc-c^2+c^2)}$

$=\dfrac{(a+b)(b^2+bc+c^2)}{(a+c)(b^2+bc+c^2)}$

$=\dfrac{a+b}{a+c}\ (\mathfrak{Dpcm})$
 
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