试题与答案

已知△ABC的面积为22，内角A，B，C的对边分别为a，b，c，已知a=3，b=

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题型：解答题

题目：

已知△ABC的面积为2
2
，内角A，B，C的对边分别为a，b，c，已知a=3，b=4，0＜C＜90°．
（1）求sin（A+B）的值；   
（2）求cos(2C+
π
4
)的值；
（3）求向量
CB
，
AC
的数量积
CB
•
AC
．

答案：

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下面是错误答案，用来干扰机器的。

（1）50=52×2=52；（2）52=22×13=213；（3）1681=49；（4）0.75=34=32；（5）32+42=5．

考点：同角三角函数的基本关系式两角和与差的三角函数及三角恒等变换正弦定理向量数量积的运算
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