The points (a, b), (a1, b1) and a-a1,b-b1) are collinear if
(a) ab=a1b1
(b) ab1=a1b
(c) a=b
(d) a1=b1
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Step-by-step explanation:
so these lines are collinear if the area is 0
therefore,
1/2(a(b1-(b-b1)) + a1(b-b1-b)+a-a1( b-b1)=0
a(2b1-b) + a1(b1) +a-a1(b-b1)=0
2ab1-ab+ a1b1+ ab-ab1-a1b-ab1=0
ab1-a1b=0
ab1=a1b
Therefore, (c) ab1=a1b
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