xét `DeltaEFK` có
`hatE+hatF+hatK=180^@`
`hatE+80^@+60^@=180^@`
`hatE+140^@=180^@`
`hatE=40^@`
ta có `hat(HEK)=hat(HEF)=hatE/2=40^@/2=20^@`
xét `DeltaEFH` có
`hat(HEF)+hatF+hat(EHF)=180^@`
`20^@+80^@+hat(EHF)=180^@`
`100^@+hat(EHF)=180^@`
`hat(EHF)=80^@`
`to`Chọn `B`