Math & Science ⇒ Alignment of equal Sign to Numerator in Fraction

[ghostanime2001]

How can I make the equal sign align in the center of 2pi in the numerator?

Code: Select all

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\[k=\dfrac{2\pi}{\lambda}\]
\end{document}