\frac{1-35\frac{y^2}{x^2}}{-2\frac{1}{y^2}+2\frac{1}{xy}} - \frac{17}{1-\frac{x}{y}} = \frac{\frac{x^2-35y^2}{x^2}}{\frac{-2x+2y}{xy}} - \frac{17y}{y-x}
= \frac{x^2-35y^2}{x^2} \cdot \frac{xy}{-2(x-y)} - \frac{17y}{y-x} = \frac{y(x^2-35y^2)}{-2x(x-y)} + \frac{17y}{x-y}
= \frac{-y(x^2-35y^2) + 34xy}{2x(x-y)} = \frac{-x^2y+35y^3+34xy}{2x(x-y)}