2.7陪集、指数和Lagrange定理 性质1:a∈aH [a∈Ha 性质2:a∈H→alH=H aeH台Ha=HI 性质3:b∈aH→bH=aH b∈Ha→Hb=Ha 性质4: aH=bH→a'b∈H(b'aeH) Ha=Hb ba1∈H(ab'eH)l 性质5:若 aH∩bH≠,则aH=bH [若Ha∩Hb≠, 则Ha=Hb]2.7 陪集、指数和Lagrange定理 性质1: [ ] 性质2: [ ] 性质3: [ ] 性质4: ( ) [ ( )] 性质5:若 ,则aH=bH [若 ,则Ha=Hb] a aH a Ha a H aH H = a H Ha H = b aH bH aH = b Ha Hb Ha = 1 aH bH a b H = − 1 b a H − 1 Ha Hb ba H = − 1 ab H − aH bH Ha Hb