证一记F()=f(an)t∈(, 22 则由题设知 lim F(t=lim f(x=A x→-0 十 lim F(t=lim f(x)=A x→+ 2 且F(1)=f(tant)sec2t在 故由①知 元元 3(22)使F(m)=tan,e2r=0 而 Sec2t≠0 →∫()=05=tan∈(-0,+∞)证一 ) 2 , 2 ( ) (tan ) (   记F t = f t t  − 则由题设知 F t f x A x t = = →−  →− + lim ( ) lim ( ) 0 2  F t f x A x t = = →+  → − lim ( ) lim ( ) 0 2  且F(t) = f (tant)sec2 t存在 故由①知 ), ( ) (tan ) sec 0 2 , 2 ( 2   − F  = f  t  t =    使 而 sec 0 2 t   f ( ) = 0  = tan (−,+)