f"(x) xcos x-sinx cos x(x-tan x) <0 f(x)在花,1上单调下降 故x=听为极大点,x=为极小点M=(巧)=22, m=f()= ∵b-a 元 244 T SInx 2√2兀 dv≤ 兀 SInx 2 < 22 cos sin ( ) x x x x f x −  = 2 cos ( tan ) x x x − x = f (x)在 ] 2 , 4 [   上单调下降, 故 4  x = 为极大点， 2  x = 为极小点, , 2 2 ) 4 (  =  M = f , 2 ) 2 (   m = f = , 2 4 4  =  −   b − a = , 4 sin 2 2 4 2 2 4             dx x x . 2 sin 2 2 1 2 4       dx x x  0