Learn about tackling essentially complicated type of equation (6)
I believe the answer is:
linear
'type of equation' is the definition.
'learn about tackling essentially complicated' is the wordplay.
'about' indicates anagramming the letters.
'tackling' is an insertion indicator (I've seen this in other clues).
'essentially' means to look at the middle letters.
The central letter of 'complicated' is 'i'.
'learn' with letters rearranged gives 'lnear'.
'lnear' enclosing 'i' is 'LINEAR'.
(Other definitions for linear that I've seen before include "-- Motor; -- equation" , "Straight; sequential" , "One-dimensional" , "Measured lengthwise" , "Consisting of lines" .)