Cho a b c ≠ 0 thỏa mãn (a + b + c) \(\left(\frac{1}{a} + \frac{1}{b} + \frac{1}{c}\right) = 1\), Cho a;b;c ≠ 0 thoả mãn \((a + b + c) \left( \frac{1}{a} + \frac{1}{b} + \frac{1}{c} \right) = 1\)