已知cos（a+π/3)=-3/5且π/6
问题描述：
已知cos（a+π/3)=-3/5且π/6
答
cos（a+π/3)=-3/5cosacosπ/3-sinasinπ/3 = -3/51/2 cosa - √3/2 sina = -3/55cosa - 5√3sina = -65cosa + 6 =5√3sina(5cosa + 6)^2 = (5√3sina)^225cos^2a+60cosa+36 = 75sin^2a25cos^2a+60cosa+36 = 75(1-...