例3求 C。 x(1+2nx) 解 x(1+2nx) d(nx) 1+2Inx d(1+2Inx) 2 1+2Inx u=1+2nx 2 ∫hm=lma+C=,h+2hx+C例3 求 . (1 2ln ) 1 dx x x  + 解 dx x x  (1+ 2ln ) 1 (ln ) 1 2ln 1 d x x  + = (1 2ln ) 1 2ln 1 2 1 d x x + + =  u = 1+ 2ln x  = du u 1 2 1 = lnu + C 2 1 ln 1 2ln . 2 1 = + x +C