cho : $\frac{1}{x}$ + $\frac{1}{y}$ + $\frac{1}{z}$ = $\frac{1}{x+y+z}$ chứng minh rằng : $\frac{1}{x^2019}$ + $\frac{1}{y^2019}$ + $\frac{1}{z^2019
cho : $\frac{1}{x}$ + $\frac{1}{y}$ + $\frac{1}{z}$ = $\frac{1}{x+y+z}$ chứng minh rằng : $\frac{1}{x^2019}$ + $\frac{1}{y^2019}$ + $\frac{1}{z^2019}$ = $\frac{1}{x^2019 + y^2019 + z^2019}$