thanks again but i am stuck on the second part , i think i didn't quite understand the question ! can you help how can normal have maximum value?
The graph represents a curve and as you move along the curve gradient of the tangent changes. This will cause gradient of normals to change as well. The question stated that the gradient of the normal has its maximum value at P which implies the
d/dx(gradient of normal) = 0.The result you obtained in the first part is actually the gradient of the normal in terms of x.
Maximum value ---> stationary value ----> d/dx = 0
Hence you need to differentiate your answer to part 1 and equate it to zero to obtain the required solution
Hope it helps