1£®ÔÚ¡÷ABCÖУ¬a²£½b²£«c²£«bc£¬Ôò∠A£½(¡¡¡¡)

A£®60°¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡                    B£®45°

C£®120°                                                D£®30°

´ð°¸¡¡C

½âÎö¡¡cosA£½£½£½£­£¬∴∠A£½120°.

2£®ÔÚ¡÷ABCÖУ¬½ÇA¡¢B¡¢CµÄ¶Ô±ß·Ö±ðΪa¡¢b¡¢c£¬ÒÑÖªA£½£¬a£½£¬b£½1£¬ÔòcµÈÓÚ(¡¡¡¡)

A£®1                                                     B£®2

C.£­1                                                D.

´ð°¸¡¡B

½âÎö¡¡ÓÉÕýÏÒ¶¨Àí£½£¬¿ÉµÃ£½£¬

∴sinB£½£¬¹Ê∠B£½30°»ò150°.ÓÉa>b£¬

µÃ∠A>∠B£¬∴∠B£½30°.

¹Ê∠C£½90°£¬Óɹ´¹É¶¨ÀíµÃc£½2.