# How do you derive the Dirac equation for momentum space?

$\require{cancel}$

\begin{align} 0 &= i \gamma^\mu \partial_\mu \psi(x) - m \psi(x) \\ &= \int \frac{d^4 k}{(2\pi)^4}e^{-i k x}\left( \gamma^\mu k_m \tilde{\psi}(k) - m \tilde{\psi}(k) \right) \\ &= \left( \gamma^\mu k_\mu - m \right)\tilde{\psi}(k), \qquad \text{i.e.} \quad (\cancel{k} - m)\tilde{\psi}(k)=0 \end{align}

How does it get from line 2 to line 3?

• I removed the picture and put in real TeX instead. Please do this in future questions so that the links can't rot later on. Please note that I did not know how to do the slash through the $k$, but did a simple Google search to find out (and got an answer for the TeX Stack Exchange!). – DanielSank Apr 18 '15 at 3:27
• cheers for the help. i am very bad at TeX coding – Clauston Joe Apr 18 '15 at 12:25