C2. Drinking alcohol is a widely accepted behavior in America, while in Saudi Arabia it is considered an imprisonable behavior. This is a difference in folkway.
【简答题】(1)将形如 . а 11 а 12 а 21 а 22 . 的符号称二阶行列式,现规定 . а 11 а 12 а 21 а 22 . =a 11 a 22 -a 12 a 21 . 试计算二阶行列式 . cos π 4 1 1 cos π 3 . 的值; (2)已知tan( π 4 +a)=- 1 2 ,求 sin2a-2co s 2 a 1+tana .