# Bragg condition ambiguity

## Main Question or Discussion Point

Hello, I have a quick question regarding the bragg condition.

I know that it is most often stated as $$2dSin \theta=n\lambda$$

But I have come across a case (Kittel chp9 pg 255, where it is written as ($$\vec{k}$$+$$\vec{G}$$)$$^{2} = k$$

I cannot really see how the vectorial case is the same as the simpler former one.
Could someone elucidate?

Thanks

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