1¡¢ÒÑÖªÊýÁÐ{a_n}Âú×ãa₁=2£¬a_n+1-a_n+1=0£¬(n∈N)£¬Ôò´ËÊýÁеÄͨÏîa_nµÈÓÚ ( * )

A£®n²+1           B£®n+1            C£®1-n              D£®3-n

2¡¢Èý¸öÊýa£¬b£¬c¼ÈÊǵȲîÊýÁУ¬ÓÖÊǵȱÈÊýÁУ¬Ôòa£¬b£¬c¼äµÄ¹ØϵΪ (  * )

A£®b-a=c-b        B£®b²=ac          C£®a=b=c            D£®a=b=c≠0

3¡¢Èôb<0<a, dÔò    £¨  *  £©

    A£®ac         B£®          C£®a+c>b+d        D£®a£­c>b£­d

4¡¢Èôa¡¢bΪʵÊý, ÇÒa+b=2, Ôò3^a+3^bµÄ×îСֵΪ £¨  *  £©

    A£®18             B£®6              C£®2            D£®2