Question 128
Find the largest natural number $n$ such that the following holds for all real numbers $a, b, c, d$:
$$
(n+2) \sqrt{a^{2}+b^{2}}+(n+1) \sqrt{a^{2}+c^{2}}+(n+1) \sqrt{a^{2}+d^{2}} \geq n(a+b+c+d)
$$
$$
(n+2) \sqrt{a^{2}+b^{2}}+(n+1) \sqrt{a^{2}+c^{2}}+(n+1) \sqrt{a^{2}+d^{2}} \geq n(a+b+c+d)
$$