I am trying to follow along a simple derivation, and I don't really get this approximation. $$L\bigg[1+\frac{\big(y\pm\frac{d}{2}\big)^2}{L^2}\bigg]^{1/2}\approx L\bigg[1+\frac{1}{2}\cdot\frac{(y\pm\frac{d}{2})^2}{L^2}\bigg]$$
This derivation assumes that $y<<L$. Is this operation some kind of taylor expansion? What is being expanded and/or what happens in that step?
(For context, this is a problem in trying to find the zones of constructive/destructive interference in a double-slit configuration.)