$a^3=n+(\sqrt[3]{n-\frac{1}{27}}+\frac{1}{3})$ $.\sqrt[3]{n-\frac{1}{27}}$ $ ( đỏ .........
$a^3=n+(\sqrt[3]{n-\frac{1}{27}}+\frac{1}{3})$ $.\sqrt[3]{n-\frac{1}{27}}$ $<n+a^2<(a+1)^3$( hiển nhiên) ( đỏ <a).........
$a^3=n+(\sqrt[3]{n-\frac{1}{27}}+\frac{1}{3})$ $.\sqrt[3]{n-\frac{1}{27}}$ $ ( đỏ .........