A beam of light travelling between the points (0, $y_0$) and $(x_1, y_1)$ in the (x, y) plane will travel along the curve y(x) where y' = dy/dx.
I have worked out that the path y(x) must satisfy the equation
the beam of light is travelling within the infinitely wide strip between y=$y_0$ and y=$2y_0$ where $y_0$>0
By substitution or otherwise, I must verify that the circular path satisfies my previous equation.
I have tried making the equations equal each other but that has come up blank I think I have to find y'(x) when I try to differentiate y(x) all I get is y'(x)=-1 and that doesn't help very much either. all help would be greatly appreciated as this question has me really stumped. feel free to adapt tags as you see fit I wasn't sure what to put for this question