Any Parallelogram Will Work Too?

Geometry Level 2

Above shows a parallellogram A B C D ABCD with E E and F F as the midpoints of the straight lines A B AB and B C BC respectively. And straight lines E D ED and F I FI are parallel to each other.

If ア is 3 cm 2 3\text{ cm}^2 , what's the area of イ?


The answer is 6.

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1 solution

Ahmad Saad
Mar 23, 2016

Extend each lines E F EF , D C DC to meet at G G .
E F A C , E F = 1 2 A C EF \parallel AC, EF = \dfrac12 AC .

Since F I E D FI \parallel ED , then I I is a midpoint of G D GD , so F I = 1 2 E D FI = \dfrac 12 ED .

E K F J , E F K J E K = F J EK \parallel FJ , EF \parallel KJ \Rightarrow EK = FJ .

F I C D E A \triangle FIC \sim \triangle DEA with ratio of similarity of 1 : 2 1:2 ,
then I C = 1 2 E A IC = \dfrac 12 EA .
I C J E A K \triangle ICJ \sim \triangle EAK with ratio of similarity of 1 : 2 1:2 .
then I J = 1 2 E K = 1 2 F J IJ = \dfrac 12 EK = \dfrac12 FJ , therefore

area of I C J = 1 4 area of E A K = 1 2 area of F C J = 3 2 cm 2 \text{ area of } \triangle ICJ = \dfrac14 \text{ area of } \triangle EAK = \dfrac12 \text{ area of } \triangle FCJ = \dfrac32 \text{ cm}^2

Then, area of E A K = 4 3 2 = 6 cm 2 \triangle EAK = 4 \cdot \dfrac32 = \boxed {6\text{ cm}^2 } .

How do we know that FI and ED are parallel? The problem doesn't state it, and the position of point I isn't indicated.

Christina Becker - 5 years, 2 months ago

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My thoughts exactly.

Chadrick Jones - 5 years, 2 months ago

Thanks. We've updated the problem statement to reflect this.

In future, if you spot any errors with a problem, you can “report” it by selecting "report problem" in the “line line line” menu in the top right corner. This will notify the problem creator who can fix the issues.

Brilliant Mathematics Staff - 5 years, 2 months ago

FI//ED , and also quadrilateral ABCD is a parallelogram doesn't stated as words.

These two conditions are illustrated in the diagram of problem not as words.

I believe that these two conditions are important as an information ,

and the questioner depends upon it's image attachment.

Ahmad Saad - 5 years, 2 months ago

Actually simply connect EF can do.The size of triangle BEF is one quarter of the size of triangle ABC.The size of triangle AEK is one sixth of the size of triangle ABC.The size of Parallelogram EKJF is one third of the size of triangle ABC. Utilizing size of CJF is 3 can set up an equation can solve it.

沂泓 纪 - 5 years, 2 months ago

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can you post your solution with a diagram'

Deepansh Jindal - 5 years, 2 months ago

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I hope I can but actually I do not know how to post a picture in the comment,so sorry.

沂泓 纪 - 5 years, 2 months ago

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@沂泓 纪 you can send it to me on facebook

Deepansh Jindal - 5 years, 2 months ago

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@Deepansh Jindal Sure,I am eager to share my answer with you.Can you give me your email address?Thanks.

沂泓 纪 - 5 years, 2 months ago

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@沂泓 纪 [email protected] you can mail your solution to this mail

Deepansh Jindal - 5 years, 2 months ago

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@Deepansh Jindal I have sent an email to you,do you receive it?

沂泓 纪 - 5 years, 2 months ago

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