A vector A is rotated by a small angle Δ θ radians (Δ θ ≪ 1) to get a new vector B. In that case | B - A | is:

A vector $\displaystyle \overrightarrow{\mathrm{A}}$ is rotated by a small angle $\displaystyle \Delta \theta$ radians $\displaystyle (\Delta \theta \ll 1)$ to get a new vector $\displaystyle \overrightarrow{\mathrm{B}}$. In that case $\displaystyle |\overrightarrow{\mathrm{B}}-\overrightarrow{\mathrm{A}}|$ is :