-Do $0\leq a,b,c\leq 1\to \left\{\begin{matrix}abc\geq 0 \\ a\geq a^2 \\ b\geq b^2 \\ c\geq c^2 \end{matrix}\right.$Bài 471. Cho $0\leq a,~b,~c\leq 1$. CMR: $a^2+b^2+c^2\leq 1+a^2b+b^2c+c^2a $
-Do đó:
$VP\geq a^2b^2+b^2c^2+c^2a^2+1-abc$
-Lại có:
$a^2b^2+b^2c^2+c^2a^2+1-abc-a^2-b^2-c^2=(1-a^2)(1-b^2)(1-c^2)\geq 0$
(do $0\leq a,b,c\leq 1$)
$\rightarrow dpcm$