a/ `hat{CAM}=hat{DBM}=60°`
`=>hat{OAB}=hat{OBA}=60°`
`=>∆ABO` đều
b/ `hat{AOB}=hat{MDB}=60°`
`=>CO // MD`
`hat{AOB}=hat{ACM}=60°`
`=>MC//OD`
`=>` Tứ giác `ODMC` là hbh.
`=>OD=MC;OC=DM`
c/ Có `hat{AMC}=hat{BMD}=60°`
`=>hat{AMD}=hat{BMC}`
`=>∆AMD=∆CMB`
`=>AD=BC`
d/ `AD=BC`
`=>DI=BK`
Mà `hat{ADM}=hat{CBM}`
`MD=MB`
`=>∆IDM=∆KBM`
`=>MI=MK`
`hat{IMD}=hat{KMB}`
`=>hat{IMD}+hat{DMK}=hat{IMK}=60°`
`=>∆MIK` đều