[Toán 8] Nâng cao

M

manhnguyen0164

$x=\dfrac{a+b}{2}, y=\dfrac{a-b}{2}$

Thế vào $x^3-y^3=(x-y)(x^2+xy+y^2)=b(\dfrac{a^2+2ab+b^2+a^2-b^2+a^2-2ab+b^2}{4})$

$=b(\dfrac{3a^2+b^2}{4})=\dfrac{3a^2b+b^3}{4}$
 
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