I assume that you already have taken both partial derivatives.

When we want to find a suitable integrating factor, sometimes it's not so easy, so we may introduce the following cases.

__CASE__ I. Integrating factor dependent of Suppose that

it's a function that depends only of

which we'll denote it by

Then, an integrating factor for the given equation is

__CASE__ II. Integrating factor dependent of

If we have that

it's only a function of

denoted by

then

is an integrating factor for the differential equation on the form

__CASE__ III. Integrating factors of the form

If they exist

and

such that

then

is an integrating factor for the differential equation mentioned previously.

__CASE__ IV. If they exist functions

y

which satisfy

then an integrating factor for the differential equation is

Note that the case IV includes to the cases I, II y III if we take

and

respectively.