Update textbook.fr.md

12.temporary_ins/96.electromagnetism-in-media/20.reflexion-refraction-at-interfaces/20.metallic-waveguides/10.main/textbook.fr.md

@@ -24,15 +24,17 @@ _TE and TM waves and their corresponding standing wave behaviour along the y axi
 
 * For TE modes (TE = transverse-electric) we have :   
    
-$`\overrightarrow{E}_{\perp}=\underbrace{-2\,E_0\,\sin(k\cdot y\cdot \cos\,\theta)}_{\large{amplitude}}
+$`\overrightarrow{E}_{\perp}=`$$`\underbrace{-2\,E_0\,\sin(k\cdot y\cdot \cos\,\theta)}_{\large{amplitude}}
 \times \sin\big(\underbrace{k\,\sin\,\theta}_{\large{wavevector}}\,z-\omega t\big)\overrightarrow{e_z}`$    
 
    
 $`\overrightarrow{B}_{\perp}=`$
 $`\left(\begin{array}{l}
 0\\
--\dfrac{2\,E_0}{c}\sin\,\theta \,\sin\,(k\cdot y \cdot \cos\,\theta)\,\sin\,(k\,\sin\,\theta\;z -\omega t)\\
--\dfrac{2\,E_0}{c}\cos\,\theta \,\cos\,(k\cdot y \cdot \cos\,\theta)\,\cos\,(k\,\sin\,\theta\;z -\omega t)
+\\
+\underbrace{-\dfrac{2\,E_0}{c}\sin\theta \,\sin\,(k\cdot y \cdot \cos\theta)}_{\large{amplitude}}\,\sin\,(\underbrace{k\,\sin\theta}_{\large{wavevector}}\,z -\omega t)\\
+\\
+\underbrace{-\dfrac{2\,E_0}{c}\cos\,\theta \,\cos\,(k\cdot y \cdot \cos\,\theta)}_{\large{amplitude}}\,\cos\,(\underbrace{k\,\sin\theta}_{\large{wavevector}}\,z -\omega t)
 \end{array}\right)`$
 
 <br>