例4求 (1+x)' x+1-1 解 (1+x) a=∫ 1+x) (1+x)2(1+x)3 jd (l+x) 1+x +C1+2(1+1y2×C 1+x"2(1+x)2例4 求 . (1 ) 3 dx x x  + 解 dx x x  + 3 (1 ) dx x x  + + − = 3 (1 ) 1 1 ] (1 ) (1 ) 1 (1 ) 1 [ 2 3 d x x x + + − + =  1 2 2 2(1 ) 1 1 1 C x C x + + + + + = − . 2(1 ) 1 1 1 2 C x x + + + + = −