表达式3: left parenthesis, "f" left parenthesis, "t" , right parenthesis , "g" left parenthesis, "t" , right parenthesis , right parenthesisft,gt
3
表达式4: "a" equals left bracket, 0 "n" , StartFraction, 2 pi Over 20 , EndFraction "n" , ...2 pi "n" , right bracketa=0n,2π20n,...2πn
4
表达式5: left parenthesis, "f" left parenthesis, "t" , right parenthesis cos left parenthesis, "a" , right parenthesis minus "g" left parenthesis, "t" , right parenthesis sin left parenthesis, "a" , right parenthesis , "f" left parenthesis, "t" , right parenthesis sin left parenthesis, "a" , right parenthesis plus "g" left parenthesis, "t" , right parenthesis cos left parenthesis, "a" , right parenthesis , right parenthesisftcosa−gtsina,ftsina+gtcosa
