Rewrite "Lagrange multiplier", various improvements

1 files changed, 3 insertions, 1 deletions

diff --git a/source/know/concept/electric-dipole-approximation/index.md b/source/know/concept/electric-dipole-approximation/index.md
index 7c710ec..35cf00c 100644
--- a/source/know/concept/electric-dipole-approximation/index.md
+++ b/source/know/concept/electric-dipole-approximation/index.md
@@ -30,6 +30,8 @@ so that $$\vb{A} \cdot \vu{P} = \vu{P} \cdot \vb{A}$$:
 
 $$\begin{aligned}
     \comm{\vb{A}}{\vu{P}} \psi
+    &= (\vb{A} \cdot \vu{P} - \vu{P} \cdot \vb{A}) \psi
+    \\
     &= -i \hbar \vb{A} \cdot (\nabla \psi) + i \hbar \nabla \cdot (\vb{A} \psi)
     \\
     &= i \hbar (\nabla \cdot \vb{A}) \psi
@@ -75,7 +77,7 @@ $$\begin{aligned}
 Where $$\vb{E}_0 = \omega \vb{A}_0$$.
 Let us restrict ourselves to visible light,
 whose wavelength $$2 \pi / |\vb{k}| \sim 10^{-6} \:\mathrm{m}$$.
-Meanwhile, an atomic orbital is several Bohr $$\sim 10^{-10} \:\mathrm{m}$$,
+Meanwhile, an atomic orbital is several Bohr radii $$\sim 10^{-10} \:\mathrm{m}$$,
 so $$\vb{k} \cdot \vb{x}$$ is negligible:
 
 $$\begin{aligned}