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## Homework Statement

Find an integrating factor for:

xdy - (y + x^2 + 9y^2)dx = 0

## Homework Equations

P(x,y)dx + Q(x,y)dy = 0

Δμ = μ

_{y}P - μ

_{x}Q.

where μ is the integrating factor.

## The Attempt at a Solution

well, I don't know what I should do. I can use the formula I wrote but that would lead to solving a PDE. any ideas?