4.1群的概念 cosacosb-sinasinb sinacosbtcosasinb sinacosb-cosasinb cosacosb-sinasinb coS(a+b)sin(a+b)=Ta+b sin(a+b)cos(a+b) 从而有(a)封闭性 (b)结合律成立 (TaTB)Ty=TIT7)= TaTTY;(c)有单位元: To 0g)有逆元:Ta=Ta cosa -sina SIna cosa4.1 群的概念 = cosacosb-sinasinb sinacosb+cosasinb -sinacosb-cosasinb cosacosb-sinasinb = cos(a+b) sin(a+b) =Ta+b -sin(a+b) cos(a+b) 从而有(a)封闭性; (b)结合律成立： (TαTβ)Tγ = Tα(TβTγ) = TαTβTγ ; (c)有单位元： T0 = ; (d)有逆元：Ta =T-a = cosa -sina sina cosa 1 0 0 1