¹®¹ÌË«»ù,ÌáÉýÄÜÁ¦

Ò»¡¢Ñ¡ÔñÌâ

1£®(2012·¸£½¨)µÈ²îÊýÁÐ{a_n}ÖУ¬a₁£«a₅£½10£¬a₄£½7£¬ÔòÊýÁÐ{a_n}µÄ¹«²îΪ(¡¡¡¡)

A£®1¡¡ ¡¡¡¡¡¡B£®2¡¡ ¡¡¡¡¡¡C£®3¡¡ ¡¡¡¡¡¡D£®4

½âÎö£ºa₁£«a₅£½2a₃£½10£¬Ôòa₃£½5£¬ËùÒÔd£½a₄£­a₃£½7£­5£½2.

´ð°¸£ºB

2£® (2012·ÁÉÄþ)ÔڵȲîÊýÁÐ{a_n}ÖУ¬ÒÑÖªa₄£«a₈£½16£¬Ôò¸ÃÊýÁÐÇ°11ÏîºÍS₁₁£½(¡¡¡¡)

A£®58                                           B£®88 

C£®143                                         D£®176

½âÎö£º·½·¨Ò»£ºS₁₁£½£½£½88.

·½·¨¶þ£ºS₁₁£½11a₆£½11×8£½88.

´ð°¸£ºB

3£®(2013·É½¶«ÁÙÒÊÖʼì)ÔڵȲîÊýÁÐ{a_n}ÖУ¬Èôa₂£«a₄£«a₆£«a₈£«a₁₀£½80£¬Ôòa₇£­a₈µÄֵΪ(¡¡¡¡)

A£®4                                            B£®6 

C£®8                                            D£®10