Update cheatsheet.md

cheatsheet.md

@@ -1,25 +1,35 @@
 ## math
-
-$π = radians(180.0) = acos(0.0) * 2.0$
-
+```
+π = radians(180.0) = acos(0.0) * 2.0
+```
 #### rule of three
 
-$\frac{x1}{x2} = \frac{?}{y2}$ -> $? = \frac{x1 * y2}{x2}$
+```
+ x1     ?          x1 * y2
+---- = ---- -> ? = -------
+ x2     y2            x2
+
+```
 
 ### 2d math
 
 
 ### trigonometry
 ```
-                                      _- \
-sin(α) = a / c                     _-   . \
-cos(α) = b / c               b  _-         \ a
-tan(α) = a / b               _-             \
-sin(β) = b / c            _-  α            β \
+                                      _-'\
+sin(α) = a / c                     _-'  . \
+cos(α) = b / c               b  _-'        \ a
+tan(α) = a / b               _-'            \
+sin(β) = b / c            _-' α            β \
 cos(β) = a / c           ----------------------
 tan(β) = b / a                     c
 ```
 
 https://www.arndt-bruenner.de/mathe/scripts/dreiecksberechnungrw.htm
 
+#### change length of a vector
+```
+normalize(vec) * newLen = vec * newLen / length(vec)
+```
 ### 3d math
+