cos72(cos72－cos12)＋sin72(sin72－sin12）答案是0.

分类: 作业答案 • 2022-05-20 20:28:51

问题描述：

答

cos^2(72)-cos72cos12+sin^2(72)-sin72sin12 =1-cos72cos12-sin72sin12 =1-cos(72-12) =1-cos60 =1/2

答

cos72(cos72－cos12)＋sin72(sin72－sin12） =[(cos72)^2+(sin72)^2]-(cos72cos12+sin72sin12) =1-cos60 =1/2