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\(\displaystyle L_\theta = L_0 ( 1 + \alpha \theta)\)

where L is the length and theta is the temperature change. The coefficient alpha is usually pretty small, 11E-6 for steel, so one ends up with a lot of numbers like 1.000011.

This is where I seem to have entered a strange world, where

\(\displaystyle \sqrt{(1 + x)} \rightarrow 1 + x/2\)

\(\displaystyle \dfrac{1}{ \sqrt{(1 - x)}} \rightarrow 1 + x/2\)

\(\displaystyle (1 - x)^3 \rightarrow 1-3x\)

Is there a name for this area of maths, and somewhere I can look up more about it?

Thanks for any help.

Perplexed