Problem

Source: 2002 Singapore TST 2.1

Tags: algebra, inequalities



Let $x_1, x_2, x_3$ be positive real numbers. Prove that $$\frac{(x_1^2+x_2^2+x_3^2)^3}{(x_1^3+x_2^3+x_3^3)^2}\le 3$$