[methods] add CAS instructions for tangent function

diff --git a/methods/calculus-ref.md b/methods/calculus-ref.md
index e12b37e76611a8ec1714f7877ef26ab7f979510e..f33315231599bc99bbd9d1a6ee8e7e655b7e6fcf 100644 (file)
--- a/methods/calculus-ref.md
+++ b/methods/calculus-ref.md
@@ -55,6 +55,8 @@ Not differentiable at:
 **Normal line** - $\perp$ tangent ($m_{{tan}} \cdot m_{\operatorname{norm}} = -1$)  
 **Secant** $={{f(x+h)-f(x)} \over h}$
 
+\colorbox{cas}{On CAS:} Action $\rightarrow$ Calculation $\rightarrow$ Line $\rightarrow$ `tanLine` or `normal`  
+
 ## Strictly increasing/decreasing
 
 For $x_2$ and $x_1$ where $x_2 > x_1$: