Forgive me if I err along the line, but PH or someone will be along to correct me if I wonder.
It's been awhile.
Now, check to see if your DE is exact.
There exists a function f(x,y), such that:
From the 1st equation, after integrating:
Take the partial derivative with respect to y of the last expression and set the result equal to N(x,y):
Check to make sure I didn't boo-boo.