3.1题：(1+x)^n=nx-1，答案为C3.2题，方法同上=0.5*tanx+0.5sinx=x4.1题，极限为3/2
(1+x^(1/3))^(1/3)-1=1+ 1/3 x^(1/3)+ O(x^(2/3))-1= 1/3 x^(1/3)+ O(x^(2/3))答案： 1/3 x^(1/3)
C
