Areas of Parallelograms and Triangles

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agnibho
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Homework Statement


ABC and BDE are two equilateral triangles such that D is the midpoint of BC. If AE intersects BC at F, show that :-
(i) ar(BDE) = 1/4 ar(ABC)
(ii) ar(BDE) = 1/2 ar(BAE)
(iii) ar(ABC) = 2ar(BEC)
(iv) ar(BFE) = ar(AFD)
(v) ar(BFE) = 2ar(FED)
(vi) ar(FED) = 1/2ar(AFC)


Homework Equations





The Attempt at a Solution


There was this hint :- [join EC and AD and then showing BE ll AC and DE ll AB,etc.]
 
I couldn't upload the diagram.
I tried to follow the hint but from there on I couldn't succeed in solving this sum.
If anyone would tell me how to do this sum I'll be pleased
 
agnibho said:
ABC and BDE are two equilateral triangles such that D is the midpoint of BC. If AE intersects BC at F, show that :-
(i) ar(BDE) = 1/4 ar(ABC)
(ii) ar(BDE) = 1/2 ar(BAE)
(iii) ar(ABC) = 2ar(BEC)
(iv) ar(BFE) = ar(AFD)
(v) ar(BFE) = 2ar(FED)
(vi) ar(FED) = 1/2ar(AFC)

There was this hint :- [join EC and AD and then showing BE ll AC and DE ll AB,etc.]

My take on your diagram attached.
To continue, what is the formula for the area of an equilateral triangle?
 
Attachments
  • Geometry diagram: triangle ABC with vertex A at top, C at left and B at right, and segment CB horizontal. Point D lies on CB, F is where AE crosses CB, and E sits below, joined to D and B, forming a triangle DEB.
    Forum2Triang.jpg
    7.8 KB · Views: 579
Area of an equilateral triangle = [tex]\sqrt{}3[/tex]/4*side2
 
agnibho said:
Area of an equilateral triangle = [tex]\sqrt{}3[/tex]/4*side2

I assume my diagram was correct?

Anyway, D is at the midpoint of BC, so BD = BC/2
Aabc = [tex]\sqrt{}3[/tex]/4*BC2
Abde = [tex]\sqrt{}3[/tex]/4*BD2 = [tex]\sqrt{}3[/tex]/4*(BC/2)2

Finish that and retry the others.