1£®ÔڵȲîÊýÁÐ{a_n}ÖУ¬Èôa₃£«a₄£«a₅£«a₆£«a₇£½450£¬Ôòa₂£«a₈µÄÖµµÈÓÚ(¡¡¡¡)

A£®45¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡                            B£®75

C£®180                                                     D£®300

½âÎö£º¡¡¡ßa₂£«a₈£½a₃£«a₇£½a₄£«a₆£½2a₅£¬

∴ÓÉÒÑÖªµÃ5a₅£½450£¬∴a₅£½90

∴a₂£«a₈£½2a₅£½180.

´ð°¸£º¡¡C

2£®ÔÚ¡÷ABCÖУ¬Èôb£½2asin B£¬Ôò½ÇAΪ(¡¡¡¡)

A£®30°»ò60°                                           B£®45°»ò60°

C£®120°»ò60°                                          D£®30°»ò150°

½âÎö£º¡¡¸ù¾ÝÕýÏÒ¶¨Àísin B£½2sin Asin B£¬