cos10-cos70 =2sin40sin30 有人会吗
问题描述:
cos10-cos70 =2sin40sin30 有人会吗
答
cos10-cos70=cos(40-30)-cos(40+30)=cos40cos(-30)-sin40sin(-30)-(cos40cos30-sin40sin30)=2sin40sin30
cos10-cos70 =2sin40sin30 有人会吗
cos10-cos70=cos(40-30)-cos(40+30)=cos40cos(-30)-sin40sin(-30)-(cos40cos30-sin40sin30)=2sin40sin30