已知△ABC的角A、B、C所对的边分别是a、b、c，设向量
（I）若
（Ⅱ）若
|
（I）∵
∥m
，∴acosB=bsinA，（2分）n
根据正弦定理得：2RsinAcosB=2RsinBsinA（4分）
∴cosB=sinB，即tanB=1，又B∈（0，π），
∴B=
；（8分）π 4
（Ⅱ）由
•m
=4得：a+b=4，（8分）p
由余弦定理可知：4=a2+b2-2abcos
=a2+b2-ab=（a+b）2-3ab，π 3
于是ab=4，（12分）
∴S△ABC=
absinC=1 2
．（13分）3
| 从方框中选择最佳选项完成对话，有两项是多余的。 | |
B: It was great. A: Where did you go? B: 1._____ A: Really? Wow! What did you do there? B: Well, we went to a lot of museums. A: Oh, how were they? B: They were really interesting. 2. _____ A: Did you go shopping? B: Yes, I did. A: 3._____ B: Oh, they were very expensive. A: And how were the people? 4._____ B: The people were really friendly. My parents have some Japanese friends, and we had dinner at their houses. A: 5._____ B: It was delicious. I love Japanese food. |