x+a +C 例17求x3√4-xa 解:令x=2snt,dx=2 cos tdt,t∈ ∫x√4-xd-(2smn)4-4sm212csth=32Jsm7cost =32 sin t(1-cost)cos tdt =-32 (cost-cosi)d cost 32( 1)+C 4-x2+4-x2+C 4 例18 求 -dx (a> 解:令x=asct,dk= sect tan tdt,t∈(0,z -dx a sec t·tant a tan t seidl=In(sec 1+ tan)+C a7 ln . 2 2 C a x a a x + + = + 例 17 求 4 . 3 2 x x dx − 解:令 x = 2sin t , dx = 2costdt, − 2 , 2 t x x dx − 3 2 4 (2sin t) 4 4sin t 2costdt 3 2 = − t tdt 3 2 32 sin cos = t t tdt 2 2 32 sin (1 cos ) cos = − 32 (cos t cos t)d cost 2 4 = − − = − t − cos t) +C 5 1 cos 3 1 32( 3 5 ( ) ( 4 ) . 5 1 4 3 4 5 2 3 2 = − − x + − x +C 例 18 求 ( 0). 1 2 2 − dx a x a 解:令 x = asect , dx = asect tantdt , 2 0, t = − dx x a 2 2 1 dt a t a t t tan sec tan = sec tdt = ln(sec t + tan t) +C ln . 2 2 C a x a a x + − = + t a x 2 2 x + a t 2 x 2 4− x