准则|′如果当x∈U(x)(或x>M)时有 (1)g(x)≤f(x)≤h(x), (2)lim g(x)=A, lim h(r)=A, x→>x0 (x→>∞0) 那末lim∫(x)存在,且等于A x→0 A+6 y=h(x) y=f(x) y=g(x) 4 0 0 +6准则Ⅰ′ 如果当 ( ) 0 0 x U x   (或 x  M )时,有 (2) lim ( ) , lim ( ) , (1) ( ) ( ) ( ), ( ) ( ) 0 0 g x A h x A g x f x h x x x x x x x = =   → → → → 那末 lim ( ) ( ) 0 f x x x x → → 存在, 且等于A. y = h(x) y = f (x) y = g(x) A−  A+  −  x0 x0 x0 +  （（ ））  1  2 A