Part (ii) and (iii). For the differentiation of tan inverse (xy), use the idea of chain rule behind implicit differentiation to solve this. Differentiating tan inverse (xy) wrt x is the same as differentiating tan inverse (xy) wrt xy multiplied by the differential of xy wrt to x. I have written this formula down for you in pencil by the side for your reference. For part (iii), you just need to differentiate both sides of the equation and isolate the dy/dx term and substitute the corresponding values of x and y to get the answer. Hope this helps! Leave a comment if you still need help / clarifications!