精选优质文档-倾情为你奉上3-1-1一、选择题1cos39cos9sin39sin9等于()A. B. C D答案B解析cos39cos9sin39sin9cos(399)cos30.2cos555的值为()A. BC. D.答案B解析cos555cos(360195)cos(18015)cos15cos(4530)(cos45cos30sin45sin30).3已知,sin,则cos等于()A. B.C D答案A解析,cos0.cos.coscoscossinsin.4若sinsin1,则cos()的值为()A0B1C1D1答案B解析sinsin1,