1750 in England
William first used the symbol for parallel.
Pythagoras was the 1st person who used the pi symbol first
William Jones first used the pi symbol (π) in 1706
"why" is not a mathematical symbol.
The first time the symbol Pi was first used for Pi was in ancient Greece in their numbers. The symbol "π" was number 80 in Greece.
William Oughtred(1574-1660) was the first to use the symbol for parallel.
Pierre
The symbol √ for the square root was first used in print in 1525 inChristoph Rudolff's Coss, which was also the first to use the then-new signs '+' and '-'
Archimedes
Archimedes
Pierre
there is no symbol, you just say angle A is adjacent to angle B