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kietlthn hasn't added any friends yet.
27-05-2019 - 15:22
Ta có: $\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=3\iff ab+bc+ca=3abc$. Khi đó: $(a-3)(b-3)(c-3)=abc-3(ab+bc+ca)+9(a+b+c)+27=abc-9abc+0+27=27-8abc$
Ta có: $\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=3\iff ab+bc+ca=3abc$.
Khi đó: $(a-3)(b-3)(c-3)=abc-3(ab+bc+ca)+9(a+b+c)+27=abc-9abc+0+27=27-8abc$
Mình nhầm là a+b+c=3