(x + 2)(x + 4)/x
= (x² + 6x + 8)/x
= x + 8/x + 6
≥ 2√(x·8/x) + 6
= 4√2 + 6
当且仅当 x = 8/x ,即 x = 2√2 时等号成立
所以最小值是 4√2 + 6