例2估计积分 ,dx的值 0 3+sinx 解f(x)= 3+sinx ,Vx∈|0,, 0≤sinx≤1, < 4-3+sin3x-3 1 dx≤ax≤dx 04 3 0 3+sIn x 3 T T < 3 0 3+sin x 3例 2 估计积分 dx x   0 + 3 3 sin 1 的值. 解 , 3 sin 1 ( ) 3 x f x + =  x[0, ], 0 sin 1, 3  x  , 3 1 3 sin 1 4 1 3  +  x , 3 1 3 sin 1 4 1 0 0 3 0 dx dx x dx        +  . 3 sin 3 1 4 0 3   +      dx x