例2设y= arctan√1+x2+ln 1+x2+1 2 1+x2-1 求 解设n=√1+x2,则y=1 arctan u+lm+1 2 L 11 2(1+u2)4a+1 2x2-x (√1+x2 y (2x+x3)1+x24 例 2 . , 1 1 1 1 ln 41 arctan 1 21 22 2 y xx y x  + − + + = + + 求设 解 1 , 2 设 u = + x , 11 ln 41 arctan 21 −+ = + uu 则 y u ) 1 1 1 1 ( 41 2(1 ) 1 2 − + + + +  = u u u y  u 4 1 1− u = , 2 12 4 − x − x = ( 1 ) 2 u = + x  x , 1 2 x x+ = . (2 ) 1 13 2 x x x y x + +   = −