ƚ  S Q .   & F & MathTypepTimes New Roman؟ww w f<-2 mx2 tbx2 ^yx2  bx2 bx2 mx2 tbx2 ^yx2 `bx2 `mx2 `^yxSymbol %؟ww w f<-2 =x2 `-x2  -x2 +x2 =x2 `-x2 `+x2 `x=x & "System< f< !-