Chapter P - Prerequisites: Fundamental Concepts of Algebra - Exercise Set P.3 - Page 49: 79

$-y\sqrt[3]{2x}$

$$\sqrt[3]{54xy^3} - y\sqrt[3]{128x}$$ $$=\sqrt[3]{27y^3\times2x} - y\sqrt[3]{64\times2x}$$ $$=\sqrt[3]{27y^3}\times\sqrt[3]{2x} - y\times\sqrt[3]{64}\times\sqrt[3]{2x}$$ $$=3y\sqrt[3]{2x} - 4y\sqrt[3]{2x}$$ $$=(3y-4y)\sqrt[3]{2x}$$ $$=-y\sqrt[3]{2x}$$