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## Homework Statement

I'm trying to follow and work through a derivation in my textbook, making sure I can replicate the steps myself and understand whats happening. However, I came across this approximation and can't seem to figure out where it comes from or why and the book gives no clues.

## Homework Equations

The general form is:

[tex]\frac{1}{a}\left(1-\frac{x}{a}\right)^{-1} \cong \frac{1}{a}\left(1+\frac{x}{a}\right) [/tex]

Could anyone please explain this to me?