ax+by=5
A點代入, a(1)+b(-1)=5,a-b=5...(1)
B點代入, a(-2)+b(-3)=5,-2a-3b=5...(2)
(1)x2+(2), (2a-2b)+(-2a-3b)=5x2+5
-5b=15, b=-3,
a-(-3)=5, a=2
2x-3y=5