Áp dụng BĐT Cô-si ta có $A= x + \frac{1}{y(x-8y)} = (x-8y)+8y+\frac{1}{y(x-8y)} \ge 3\sqrt[3]{(x-8y).8y.\frac{1}{y(x-8y)}}=6$Suy ra $\min A =6 \Leftrightarrow (x-8y)=8y=\frac{1}{y(x-8y)} \Leftrightarrow x = 4, y=\frac{1}{4}.$
Áp dụng BĐT Cô-si ta có $A= x + \frac{1}{y(x-8y)} = (x-8y)+8y+\frac{1}{y(x-8y)} \ge 3\sqrt[3]{(x-8y).8y.\frac{1}{y(x-8y)}}=6$Suy ra $\min A =6 \Leftrightarrow (x-8y)=8y=\frac{1}{y(x-8y)} \Leftrightarrow x = 2, y=\frac{1}{4}.$
Áp dụng BĐT Cô-si ta có $A= x + \frac{1}{y(x-8y)} = (x-8y)+8y+\frac{1}{y(x-8y)} \ge 3\sqrt[3]{(x-8y).8y.\frac{1}{y(x-8y)}}=6$Suy ra $\min A =6 \Leftrightarrow (x-8y)=8y=\frac{1}{y(x-8y)} \Leftrightarrow x =
4, y=\frac{1}{4}.$