Without seeing the exact question, it's difficult to say.
dxdy = dydx, and the order of integration doesn't matter, so you can do it either way.
However, of course, if the question insists on integrating wrt x first, then it's checking whether you know how to get the limits (which you don't, yet!
), and of course you must do it that way.
So, what are the limits for x (they are functions of y
) if you integrate wrt x first?
(in other words, for a fixed value of y
, what are the limits of x?)