I tried to find IF by doing the following but I got stuck since I cannot obtain a solution with one valiable. What should I do or how can I obtain IF with different method ( I tried to do y = vx, v + x*dv/dx = M/N, too but did not work either) ?

d(x^5*y^7 - x^3*y)/dy = 7*x^5*y^6 - x^3

d(x^6*y^6 + x^4)/dx = 6*x^5*y^6 + 4*x^3

[(6*x^5*y^6 + 4*x^3) - (7*x^5*y^6 - x^3)]/(x^5*y^7 - x^3*y)

= [1*(5 - x^2*y^6)]/[y*(x^2*y^6 - 1)] --> still has both x and y

[(7*x^5*y^6 - x^3)- (6*x^5*y^6 + 4*x^3)]/(x^6*y^6 + x^4)

= [1*(x^2*y^6 -5)]/[x*(x^2*y^6 + 1)] --> still has both x and y

I'm taking a correspondence course, so this is the only place I can get help. So someone please help me!