Taking the Middle

Geometry Level 2

What figure do you get when you connect up the midpoints of consecutive sides of a quadrilateral?

Rectangle None of the rest Rhombus Parallelogram Kite

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2 solutions

By the Midpoint Theorem we know that joining the midpoints of two consecutive sides will form a line segment that is parallel to and half the length of a diagonal of the original quadrilateral. As there are only two diagonals, the figure created by joining the (consecutive) midpoints of the original quadrilateral will have two pairs of parallel sides, which implies that the figure is a parallelogram.

(The figure created could be a rectangle or rhombus if the original quadrilateral is itself a parallelogram, but this is not the case in general. Also, note that by "diagonal" I mean the line segment joining two non-consecutive vertices, (clockwise or counterclockwise), of the original quadrilateral.)

Sir, I think it would be better understandable to beginners if you mention 'Midpoint Theorem' in your solution.

Venkata Karthik Bandaru - 6 years, 1 month ago

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Thanks for the suggestion, Karthik. I've made the edit and added a link. :)

Brian Charlesworth - 6 years, 1 month ago

@Calvin Lin Do you think it should be phrased as "... midpoints of consecutive sides of a quadrilateral?"

Brian Charlesworth - 6 years, 1 month ago

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Edited. Thanks!

Calvin Lin Staff - 6 years, 1 month ago
Kaleem Ullah
May 26, 2015

both of the opposite lines must be parallel in parallelogram which is the exact case over here . while in case of trapezoid only one opposite line is parallel.

Why must it be a parallelogram? Why can't it be a trapezoid?

Calvin Lin Staff - 6 years ago

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both of the opposite lines must be parallel in parallelogram which is the exact case over here . while in case of trapezoid only one opposite line is parallel.

Kaleem Ullah - 6 years ago

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Great! That explanation should be included in your solution, for it to be complete.

You can edit your solution by clicking on the "Edit" button at the bottom of the solution.

Calvin Lin Staff - 6 years ago

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