$\text{K=$\dfrac{1}{4}$ +$\dfrac{1}{12}$+...+ $\dfrac{1}{112}$}$
$\text{⇒K=$\dfrac{1}{4}$(1+ $\dfrac{1}{3}$+...+ $\dfrac{1}{28}$ )}$
$\text{Xét 1+ $\dfrac{1}{3}$+...+ $\dfrac{1}{28}$}$
$\text{⇒1>1+$\dfrac{1}{28}$}$
$\text{⇒$\dfrac{1}{3}$>$\dfrac{1}{28}$}$
$\text{⇒$\dfrac{1}{28}$=$\dfrac{1}{28}$ (Có 7 số hạng)}$
$\text{nên 1+ $\dfrac{1}{3}$+...+ $\dfrac{1}{28}$>$\dfrac{1}{28}$×7=$\dfrac{1}{4}$}$
$\text{Do đó:K=$\dfrac{1}{4}$(1+ $\dfrac{1}{3}$+...+ $\dfrac{1}{28}$ )>$\dfrac{1}{4}$×$\dfrac{1}{4}$=$\dfrac{1}{16}$}$
$\text{Vậy K>$\dfrac{1}{16}$}$
