Chứng minh AD song song KC. Chứng minh BD < DC
Cho tam giac ABC (AB<AC).Tren tia doi cua tia AC lay E dao cho AB=AE; tren tia doi cua tia AB lay K sao cho AK=AC
a, Ve phan giac AD. CM AD song song KC
a, Ve phan giac AD. CM AD song song KC
c BD<DC
CAI Y c y mik cm the nay ne:
Tren canh AC lay F sao cho AB=AF
Tam giac ABD=tam giac AFD(c-g-c)
BD=DF; goc ABD=goc AFD
VI AB<AC nen goc ABD>goc ACB
goc AFD>goc ACB
goc AFD=goc FDC+goc FCD
goc AFD va goc DFC ke bu
goc DFC la goc tu
goc DFC>goc FCD
DF<DC
BD<DC
CAI Y c y mik cm the nay ne:
Tren canh AC lay F sao cho AB=AF
Tam giac ABD=tam giac AFD(c-g-c)
BD=DF; goc ABD=goc AFD
VI AB<AC nen goc ABD>goc ACB
goc AFD>goc ACB
goc AFD=goc FDC+goc FCD
goc AFD va goc DFC ke bu
goc DFC la goc tu
goc DFC>goc FCD
DF<DC
BD<DC