例2求 3+2x 解 (3+2x), 3+2x 2 3+2x = 3+2x2J3+2x (3+2x) du =Inu+C=In(3+ 2x)+C 2 2 般地∫f(ax+bhl ∫(u)ldn u=ax+b例2 求 . 3 2 1 dx x  + 解 (3 2 ) , 3 2 1 2 1 3 2 1  +  + =  + x x x dx x  3 + 2 1 x dx x (3 2 ) 3 2 1 2 1  +  + =  du u  = 1 2 1 = lnu + C 2 1 ln(3 2 ) . 2 1 = + x + C  f (ax + b)dx =  u du u=ax+b f a [ ( ) ] 1 一般地