They are all fatty acids. Chemists isolated a long-chain saturated fatty acid from peanuts, which is 20 carbonic acid and is defined as arachidic acid. Later, a large number of fatty acids with 20 carbon chains were discovered. According to the number of olefinic bonds, Chinese chemists called them peanut isooctanoic acid for short. Arachidonic acid is a fatty acid with 20 carbon chains, and its chemical name is eicosapentaenoic acid.