(x)h==l((当x=a时=a,当x=b时 例2计算[2 coS xsin xdx 解 2 coS xsin xdx=-12 coS xd cosx 令cosx=t , rdt=5 或 coSxSInxax cos xa cosx cOSx 2 COS-+-COS 0 26 换元一定要换积分限,不换元积分限不变 首页 上页返回 结束 铃首页 上页 返回 下页 结束 铃 例 2 计算 cos xsin xdx 2 5 0   例2  解 cos xsin xdx cos xd cosx 2 5 0 2 5 0   =−   cos xsin xdx cos xd cosx 2 5 0 2 5 0   =−   cos xsin xdx cos xd cosx 2 5 0 2 5 0   =−   6 1 cos 0 6 1 2 cos 6 1 cos ] 6 1 [ 6 6 2 0 6 =− =− + =   x  6 1 cos 0 6 1 2 cos 6 1 cos ] 6 1 [ 6 6 2 0 6 =− =− + =   x  6 1 ] 6 1 [ 1 0 6 1 0 5 0 1 5 cos − = = =   = t dt t dt t 令 x t  6 1 ] 6 1 [ 1 0 6 1 0 5 0 1 5 cos − = = =   = t dt t dt t 令 x t  6 1 ] 6 1 [ 1 0 6 1 0 5 0 1 5 cos − = = =   = t dt t dt t 令 x t  6 1 ] 6 1 [ 1 0 6 1 0 5 0 1 5 cos − = = =   = t dt t dt t 令 x t  6 1 ] 6 1 [ 1 0 6 1 0 5 0 1 5 cos − = = =   = t dt t dt t 令 x t  cos xsin xdx cos xd cosx 2 5 0 2 5 0   =−   或 提示： 当 x=0 时 t=1, 当 2  x= 时 t=0 f x dx f t t dt b x t a ( ) [ ( )] ( ) ( )    a     令 = (当 x=a 时 t=a, 当 x=b 时 t=) 换元一定要换积分限,不换元积分限不变 下页