lean_workbook_plus_29419

In the case $n=2$, we have to prove \n $\frac{1}{x_1}+\frac{2}{x_1+x_2}<2\left(\frac{1}{x_1}+\frac{1}{x_2}\right)$ this is equivalent with \n $0<x_1(x_1+x_2)+x_1^2+x_2^2$