Symbolic maths (7)
I believe the answer is:
algebra
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">symbolic maths</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for algebra that I've seen before include "Symbol-based mathematical calculation" , "'Branch of mathematics, uses letters and symbols (7)'" , "Maths with letters representing numbers" , "Branch of mathematics using letters and symbols" , "Numbers and letters branch of maths" .)