F()sxf(x)f(tdt-f(xoy(tdt f(x(x-t)f(t)de (x)= f(t)dt f∫(x)>0,(x>0) f(t)dt>0 (x-t)f()>0,∴”(x-)f()d>0, F(x)>0(x>0) 故F(x)在(0,+∞)内为单调增加函数( ) , ( ) ( ) ( ) ( ) ( ) 2 0 0   −  = x x f t dt f x x t f t dt F x  f (x)  0, (x  0) ( ) 0, 0   x f t dt ( ) 2 0 0 0 ( ) ( ) ( ) ( ) ( ) ( )    −  = x x x f t dt xf x f t dt f x tf t dt F x (x − t) f (t)  0, ( ) ( ) 0, 0  −  x x t f t dt F(x)  0 (x  0). 故F(x)在(0,+)内为单调增加函数