diff --git a/Trigonometri.md b/Trigonometri.md
index 67d393a..a75978f 100644
--- a/Trigonometri.md
+++ b/Trigonometri.md
@@ -6,6 +6,10 @@
 	- Ex: $$\begin{align}180^\circ=\pi\text{ rad}\\\frac{\pi}{3}\text{ rad}=30^\circ\\\frac{\pi}{4}\text{ rad}=45^\circ\\\frac{\pi}{3}\text{ rad}=60^\circ\\\frac{\pi}{2}\text{ rad}=90^\circ\\2\pi\text{ rad}=360^\circ\end{align}$$
 - The right angled triangle
 	- **Def**: *The trigonometric functions: *$$\begin{align}\sin\theta=\frac{\text{perpendicular}}{\text{hypotenuse}}\\\cos\theta=\frac{\text{base}}{\text{hypotenuse}}\\\tan\theta=\frac{\text{perpendicular}}{\text{base}}\end{align}$$
+	- In addition to above, $\csc\theta=\frac{1}{\sin\theta},\sec\theta=\frac{1}{\cos\theta},\cot\theta=\frac{1}{\tan\theta}$
+	- Pythagoras' formula: $p^2+b^2=h^2$
+	  which leads to the **trigonometric identity**: $\sin^2\theta+\cos^2\theta=1$
+	  and also $\tan^2\theta+1=\sec^2\theta$
 	- Dominains and ranges:
 		- $D_{\sin}=\mathbb{R}\;\;R_{\sin}=[-1,1]$
 		- $D_{\cos}=\mathbb{R}\;\;R_{\cos}=[-1,1]$