题目

化简-2cos(A+B). 答案：解:原式=-2cos(A+B)=点评：角度的变换是三角恒等变形首先要关注的,解答本题的关键是抓住题中角之间的关系,2A+B=(A+B)+A,正确地选择公式变形.________ my surprise, ________ I could have a word with him, he left.A.In; beforeB.To; beforeC.In; whenD.To; since