do thi (s,t) ;( km,h)
os<=>Oy ; ot <=>ox
A =O(0;0) <=>(7h)
....
do thi xe thu 1 :∆1: S(t)=40t
do thi xe thu 2: ∆2: S(t)=60t-30
ve hai duong thang ∆1&∆2= cach xac dinh hai diem
D1(0;0)&D2(1;40) noi D1 voi D2=>∆1
E1(1/2;0) ;&E2(1;30) noi E1 voi E 2 keo dai ve phia E2=>∆2
∆1 x ∆2 =G
tu G ke //Ox cat Oy(AS) tai B
tu G ke //0y cat ox (At) tai C
gia tri yB chinh la khoang cach AB
gi tri xC chinh la thoi gian gap nhau
thoi diem=xc +7(h)
....
ve chuan =>yB=60(km)
xC =1,5 (h)
thoi diem gap nhau luc 8h30'