Update FOC_routine.md

Author: askuric

docs/simplefoc_library/digging_deeper/theory/FOC_routine.md

@@ -54,6 +54,9 @@ Inverse Park transformation:<br>
 Inverse Clarke transformation:<br>
 <img src="../extras/Images/inverse_clarke.png" style="margin-left:50px;margin-top:10px;margin-bottom:10px;width:180px">
 
+$u_a = U_{\alpha}$
+$u_b = \frac{-U_{\alpha} + \sqrt{3}U_{\beta}}{2}$
+$u_c = \frac{-U_{\alpha} - \sqrt{3}U_{\beta}}{2}$
 
 Here is the code of implementation of the Sinusoidal PWM in the <span class="simple">Simple<span class="foc">FOC</span>library</span>:
 ```cpp
@@ -229,4 +232,4 @@ But every motor is a bit different and you can check these values empirically on
 
 ## Further read
 
-For more info about the initialization procedure, real-time execution and the implementation details please visit [FOC implementation docs](foc_implementation).
+For more info about the initialization procedure, real-time execution and the implementation details please visit [FOC implementation docs](foc_implementation).