Bonjour,
1)
A=(0,2), B=(3,3) =>m=(3-2)/(3-0)=1/3 (AB): y-2=1/3x=>y=x/3+2
C=(0,-3), D=(1,-5)=>m=(-5+3)/(1-0)=-2 (CD): y+3=-2x=>y=-2x-3
2) ayant une mauvaise vue, je dirais (-2,1)
3)y=x/3+2
y=-2x-3
=> x/3+2=-2x-3
=>7/3x=-5
=>x=-15/7 et y= -15/7/3+2=-5/7+2=9/7
(-15/7,9/7)