Update cheatsheet.en.md

01.curriculum/01.physics-chemistry-biology/03.Niv3/02.Geometrical-optics/02.geometrical-optics-foundings/01.concept-ray-of-light/02.concept-ray-of-light-overview/cheatsheet.en.md

@@ -42,9 +42,8 @@ Dependency : **$`n \; = \; n (\nu) \; \; \; `$**, or **$` \; \; \; n \; = \; n (
 I wanted to make this important remark here, but it is not simple: with Doppler effect, medium of propagation does not move with respect to the observer ... I must think to make the warning in the main text, and a summary of all this in for example a parallel 1:
 
 !!!! ATTENTION: the $`\nu`$ frequency of a wave (temporal magnitude) measured by a given observer does not depend on the propagation 
-!!!! medium in which the measurement takes place. This is not the case of the measured wavelength $`\lambda`$, which depends on the propagation medium 
-!!!! because the propagation speed of the $V$ wave may depend on this medium. Frequency, wavelength and speed of propagation of a wave are related
-!!!! by the equation $'\lambda\: = \: \frac{V}{\nu}'$, but : <br>
+!!!! medium in which the measurement takes place. This is not the case of the measured wavelength $`\lambda`$, which depends on the propagation medium because the propagation speed of the $V$ wave may depend on this medium. Frequency, wavelength and speed of propagation of a wave are related
+!!!! by the equation $'\lambda\;=\;\dfrac{V}{\nu}'$, but : <br>
 !!!! the **fundamental quantity** (independent of the middle) is the **frequency $`\nu`$ (the temporal magnitude)**.
 -->
 
@@ -69,6 +68,6 @@ I wanted to make this important remark here, but it is not simple: with Doppler
 Optical path along a path between 2 fixed points A and B :
 **$`\delta\;=\;\int_{P \in \Gamma}\mathrm{d}\delta_P\;=\;\int_{P \in \Gamma}n_P\cdot\mathrm{d}s_P`$**
 
-* **$`\delta`$** $`=\directstyle\int_{\Gamma}n\cdot\mathrm{d}s\;=\;\int_{\Gamma}\frac{c}{v}\cdot\mathrm{d}s`$ = $`c\;\int_{\Gamma}\frac{\mathrm{d}s}{v}`$ = *$`\;c\;\tau`$*
+* **$`\delta`$** $`=\displaystyle\int_{\Gamma}n\cdot\mathrm{d}s\;=\;\int_{\Gamma}\frac{c}{v}\cdot\mathrm{d}s`$ = $`c\;\int_{\Gamma}\frac{\mathrm{d}s}{v}`$ = *$`\;c\;\tau`$*
 * **$`\delta`$** is *proportional to the travel time*.