diff --git a/01.curriculum/01.physics-chemistry-biology/02.Niv2/04.optics/04.use-of-basic-optical-elements/01.plane-refracting-surface/02.plane-refracting-surface-overview/cheatsheet.en.md b/01.curriculum/01.physics-chemistry-biology/02.Niv2/04.optics/04.use-of-basic-optical-elements/01.plane-refracting-surface/02.plane-refracting-surface-overview/cheatsheet.en.md
index b0927a932..0dd8733f0 100644
--- a/01.curriculum/01.physics-chemistry-biology/02.Niv2/04.optics/04.use-of-basic-optical-elements/01.plane-refracting-surface/02.plane-refracting-surface-overview/cheatsheet.en.md
+++ b/01.curriculum/01.physics-chemistry-biology/02.Niv2/04.optics/04.use-of-basic-optical-elements/01.plane-refracting-surface/02.plane-refracting-surface-overview/cheatsheet.en.md
@@ -162,4 +162,30 @@ You know $`\overline{SA_{obj}}`$, $`n_{inc}`$ and $`n_{eme}`$, you have previous
 ! Copy this result into (equ.2) leads to $`\overline{M_T}=+1`$.
 
 
-#### Graphical study
\ No newline at end of file
+#### Graphical study
+
+##### 1 - Determining object and image focal points
+
+Positions of object focal point F and image focal point F’ are easily obtained from the conjunction equation (equ. 1).
+
+* Image focal length $`\overline{OF'}`$ : $`\left(|\overline{OA_{obj}}|\rightarrow\infty\Rightarrow A_{ima}=F'\right)`$<br>
+&nbsp;&nbsp;&nbsp;&nbsp;(equ.1)$`\Longrightarrow\dfrac{n_{eme}}{\overline{SF'}}=\dfrac{n_{eme}-n_{inc}}{\overline{SC}}\Longrightarrow\overline{SF'}=\dfrac{n_{eme}\cdot\overline{SC}}{n_{eme}-n_{inc}}`$
+
+* Object focal length $`\overline{OF}`$ : $`\left(|\overline{OA_{ima}}|\rightarrow\infty\Rightarrow A_{obj}=F\right)`$<br>
+&nbsp;&nbsp;&nbsp;&nbsp;(equ.1) $`\Longrightarrow-\dfrac{n_{inc}}{\overline{SF}}=\dfrac{n_{eme}-n_{inc}}{\overline{SC}}\Longrightarrow\overline{SF}=-\dfrac{n_{inc}\cdot\overline{SC}}{n_{eme}-n_{inc}}
+`$
+
+##### 2 - Thin spherical refracting surface representation
+
+* **Optical axis = revolution axis** of the refracting surface, positively **oriented** in the direction of 
+propagation of the light (from the object towards the refracting surface)
+
+* Thin spherical refracting surface representation :<br><br>
+\- **line segment**, perpendicular to the optical axis, centered on the axis with symbolic 
+**indication of the direction of curvature** of the surface at its extremities.<br><br>
+\- **vertex S**, that locates the refracting surface on the optical axis.<br><br>
+\- **nodal point C = center of curvature**.<br><br>
+\- **object focal point F and image focal point F’**.
+
+
+