Virial Expansion, Van Der Waals Gas

[unscientific]

Homework Statement

Taken from 'Concepts in Thermal Physics':

Homework Equations

The Attempt at a Solution

For the step highlighted in red, why does the '-1' go into the integrand?

 

[Naz93]

1 integrated over the space gives the volume of the space. Divide that by the factor 1/V^N outside the integral and you get minus one. Hence cancelling the plus one outside the integral.