Cauchy-Schwarz Inequality problems Let $a,$ $b,$ $c,$ $d,$ $e,$ $f$ be nonnegative real numbers.
(a) Prove that
$$(a^2 + b^2)^2 (c^4 + d^4)(e^4 + f^4) \ge (ace + bdf)^4.$$
(b) Prove that
$$(a^2 + b^2)(c^2 + d^2)(e^2 + f^2) \ge (ace + bdf)^2.$$
I'm not sure how I should start approaching both problems. I believe I should use Cauchy-Schwarz, but I'm not sure.
Any help would be appreciated! Thanks in advance.

These are both CS inequality applications, you should try yourself.  Here is the first one:

*

*$(c^4+d^4)(e^4+f^4) \geqslant (c^2e^2+d^2f^2)^2$

*$(a^2+b^2)(c^2e^2+d^2f^2) \geqslant (ace+bdf)^2$
Now combine the two to get what you want.
