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**"The net flux through ANY closed surface surrounding a point charge q is given by q/"permittivity of free space" and is independent of the shape of that surface."**

I'm having a little trouble understanding this... when my book derived this formula, it did so by using the surface area of a sphere "4*pi*r^2" which made things cancel out and simplify out to q/"permittivity of free space"... so how does this equation still apply to ANY closed surface even if it's not a sphere? because I thought flux was proportional to the number of electric field lines going through a certain surface area, so the magnitude of the surface area still should matter...

a clarification would be great!