$\begin{array}{1 1}(a)\;\large\frac{a^2x}{x_1}+\frac{b^2y}{y_1}\normalsize= a^2-b^2\\(b)\;\large\frac{a^2x}{x_1}-\frac{b^2y}{y_1}\normalsize= a^2-b^2\\(c)\;\large\frac{a^2x}{x_1}+\frac{b^3y}{y_1}\normalsize =a^3-b^3\\(d)\;\text{None of these}\end{array}$