性质2单1/(x)士8(x)=f(x)士(x)在 证 f(x)±g(x)x im∑f(5;)±g(5)△x ->0 =lim∑f(5)Ax1±im∑g(5)Ax b f(x)d±g(x)dx (此性质可以推广到有限多个函数作和的情况)证   b a [ f (x) g(x)]dx i i i n i =  f  g x = → lim [ ( ) ( )] 1 0    i i n i =  f x = → lim ( ) 1 0   i i n i  g x = → lim ( ) 1 0   =  b a f (x)dx ( ) .   b a g x dx   b a [ f (x) g(x)]dx=  b a f (x)dx  b a g(x)dx . （此性质可以推广到有限多个函数作和的情况） 性质2