5. 已知平面上兩點A(2,5)，B(5,4)，則下列哪些直線會與線段AB相交?(請寫出直線代號，並且說明為何會相交) L1:y−3=x−3 L2:y−3=1/3(x−3) L3:y−3=−1/2(x−3) L4:y−3=−3(x−3)?

you may need a graph paper for drawing the points/lines
For L1,
when x=2,y=2; x=5,y=5
in graph paper,L1 cross the line
For L2
when x=2,y=2.67, x=5,y=3.67
in graphpaper,L2 do not cross the line
For L3
when x=2,y=3.5, x=5,y=2
in graph paper, L3 do not cross the line
For L4,
when x=2,y=6, x=5,y=-3
in graph paper, L4 cross the line
conclusion, L1 and L4 cross the line

全部都會相交吧

平面上，斜率不一樣的直線就會相交
先把直線AB的斜率算出來
再把L1~L4分別移項、算出斜率
因爲L1~L4斜率都跟直線AB不一樣，所以會相交