(2)y=3c0sx·lnx y=3(c0sx·Inx) 3(cos x). Inx+ cos x (Inx) = 3-sin x In x+cosx (3)y= 1+x (2-x)(1+x2)-(2-x)(1+ J (1+x2) (1+x2)-(2-x)·2x (1+x2)2 4x-1 (1+x2)28 （2） y xx = ⋅ 3cos ln y ′ = ⋅ 3(cos ln ) x x ′ = ⋅+ 3[ ln cos ] (cos ) (ln ) x x ′ x x ⋅ ′ ] 1 3[ sin ln cos x = − x ⋅ x + x ⋅ 2 1 2 x x y + − = 2 2 2 2 (2 ) (1 (1 ) (2 ) ) ) (1 x x x x y x ′ + − ′ ′ + − = − + 2 2 2 (1 ) (1 ) (2 ) 2 x x x x + − + − − ⋅ = 2 2 2 (1 ) 4 1 x x x + − − = （3）