cho goc bet xOy.tren tia Ox lay diem A sao cho Oa = 3cm.Tren tia Oy lay diem B sao cho Ob = 3cm
a,O la trung diem cua AB la dung hay sai ? vi sao
b,goi i la 1 diem nam ngoai duong thang Xy.ve cac tia Ia ia,ib,io.gia su aio = 40 do,aib = 90 do.tinh oib
c,ke ten cac cap goc ke bu trong hinh ve
help meeeeeeeeee...................