表达式3: "f" Subscript, "e" , Baseline left parenthesis, "x" , right parenthesis equals 1 half left parenthesis, "f" left parenthesis, "x" , right parenthesis plus "f" left parenthesis, negative "x" , right parenthesis , right parenthesisfex=12fx+f−x
3
表达式4: "f" Subscript, "o" , Baseline left parenthesis, "x" , right parenthesis equals "f" left parenthesis, "x" , right parenthesis minus "f" Subscript, "e" , Baseline left parenthesis, "x" , right parenthesisfox=fx−fex