The expression in (a) is not exact. Hence (a) is the correct answer.
Remark : Note that expression in (a)

Comments about Integrating Factor
Definition : Suppose that tne differential equation. M dx + N dy = 0 ...(i)
is not exact but the differential equation

is exact, where μ = F(x, y) for a suitably chosen function F. Then μ is called an integrating factor of the differential equation (i).
Ex. : The differential equation
(3ty + 4xy
2) dx + (2x + 3x
2y) dy = 0 ...(ii)
is not exact. But if we choose
μ = x
2 y.
then the differential equation

becomes exact.
∴ μ = x
2 y is an integrating factor of (ii).
Rules for finding an Integrating Factor :
Rule : 1: If Mx ± Ny ≠ 0. and is homogeneous in x and y then the integrating factor is
Ex. : Consider the differential equation
(x
2y - 2xy
2)dx- (x
3 - 3x
2y)dy = 0 ...(iii)
verify that
(i) equation (iii) is noi exact and (ii)

Intergrating factor is given by

Hence the equation

should be exact. Now equation (iv) can be written as

Rule : 2. If

is a function of x alone, say f(x), then the integrating factor μ is given by
Rule : 3. If

is a function of y alone, say φ(y), then the integrating factor μ is given by
