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If the points $(P,Q)$, $(M,N)$ and $(P-M,Q-N)$ are collinear. Then show that $QM=PN$.

  Basic Points and formulae:

  • Distance between two points = $\sqrt{(x_2-x_1)^2+(y_2-y_2)^2} $

Where, $(x_1,y_1)$ and $(x_2,y_2)$ are the coordinates of the two points.

  • The collinear points lie on the same line.
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1 Answer

up vote 1 down vote accepted

Hint: If your points are collinear, then the line through $(P,Q)$ and $(M,N)$ has the same slope as the line through $(P,Q)$ and $(P-M,Q-N)$. (They are, after all, the same line.)

There is a small thing you have to be careful about, and deal with separately. If $M-Q=0$, that is, if $M=Q$, the line is vertical.

For the case when $M-Q\ne 0$, use the standard formula for the slope of a line, and some algebra, to reach the desired conclusion.

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