AM-GM inequality basic

$a, b, c$ are positive real numbers.

Prove that $$8abc\le (a+b)(b+c)(c+a)$$

I haven't really gotten anywhere, just tried to open up $(a+b)(b+c)(c+a)$ and got null.


It's really as simple as noting that $a+b\geq 2\sqrt{ab}$, and similarly for $a+c$ and $b+c$, then multiplying it out.


Using AM-GM, we get that $$\frac{a+b}{2} \geq \sqrt{ab} $$ $$\Rightarrow a+b \geq 2 \sqrt{ab}$$

Similar manipulations show that
$$ b+c \geq 2 \sqrt{bc}$$ $$ a+c \geq 2 \sqrt{ac}$$

Multiplying all these inequalities together ( this is allowed here, since all numbers involved are positive), we get $$ \begin{align} (a+b)(b+c)(a+c) &\geq (2\sqrt{ab})(2\sqrt{bc})(2\sqrt{ac}) \\ &= 8 \sqrt{ab.bc.ac} \\ &= 8 \sqrt{a^{2} b^{2} c^{2}} \\ &= 8abc \end{align} $$ as required.