Question 1203418
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I'm not sure why the other tutors have a problem with "addition of line segments".<br>
The three points are collinear if (and only if) the length of AC is the sum of the lengths of AB and BC.<br>
AB: {{{sqrt(2^2+1^2)=sqrt(5)}}}<br>
BC: {{{sqrt(6^2+3^2)=sqrt(45)=3sqrt(5)}}}<br>
AC: {{{sqrt(8^2+4^2)=sqrt(80)=4sqrt(5)}}}<br>
{{{AB+BC=sqrt(5)+3sqrt(5)=4sqrt(5)=AC}}}<br>
The three points are collinear.<br>