下载APP
【简答题】
(Ⅰ)①证明两角和的余弦公式C(α+β)：cos(α+β)=cosαcosβ-sinαsinβ；②由C(α+β)推导两角和的正弦公式S(α+β)：sin(α+β)=sinαcosβ+cosαsinβ；(Ⅱ)已知△ABC的面积
，且
，求cosC。
参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】Task 1 Directions: After reading the following passage, you will find 5 questions or unfinished statements, numbered 36 through 40. For each question or statement there are 4 choices marked A, B, C, a...
A.
in his mind
B.
in his laboratory
C.
with microscope
D.
with telescopes