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# A regular hexagon has a perimeter of 30 units. What is the

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A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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30 Apr 2012, 01:02
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A regular hexagon has a perimeter of 30 units. What is the sum of the lenghts of all its diagonals ?

Sorry, I can't recall the answer choices but am sure answer 30 is incorrect one.
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Re: Hexagon sum of lengths of diagonals [#permalink]

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30 Apr 2012, 01:27
In a regular hexagon length of each diagonal is twice of each side.Since there are 3 diagonals and 6 sides, sum of lengths of diagonals will be equal to perimeter of hexagon.You can think a hexagon as six equilateral triangles joined together.

Hope it helps..
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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30 Apr 2012, 03:23
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gmihir wrote:
A regular hexagon has a perimeter of 30 units. What is the sum of the lenghts of all its diagonals ?

Sorry, I can't recall the answer choices but am sure answer 30 is incorrect one.

Look at the diagram below:
Attachment:

Hexagon.png [ 17.48 KiB | Viewed 8079 times ]

There are 9 diagonals in a hexagon.

Each of 3 red diagonals equal to $$2*side=2*5=10$$ (since regular hexagon is made of 6 equilateral triangles);
Each of 6 blue diagonals equal to $$2*(side*\frac{\sqrt{3}}{2})=5\sqrt{3}$$ (notice that in 30°, 60°, 90° triangle, where the sides are always in the ratio $$1 : \sqrt{3}: 2$$, half of the blue diagonal is the leg opposite 60°, so it equals to $$side*\frac{\sqrt{3}}{2}$$);

So, the sum of the lenghts of all diagonals is $$3*10+6*5\sqrt{3}=30(1+\sqrt{3})$$.

Hope it's clear.
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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03 May 2012, 21:53
Another good example of Deception, Excellent question and excellent explanation by bunuel. The ratio of the sides are deduced from the SINE FORMULA ie (a/sinA)=(b/sinB)=(c/sinC).
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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29 Jun 2013, 22:44
Bunuel wrote:
Each of 6 blue diagonals equal to $$2*(side*\frac{\sqrt{3}}{2})=5\sqrt{3}$$ (notice that in 30°, 60°, 90° triangle, where the sides are always in the ratio $$1 : \sqrt{3}: 2$$, half of the blue diagonal is the leg opposite 60°, so it equals to $$side*\frac{\sqrt{3}}{2}$$);

Bunuel: Can you please explain the above mentioned step in detail. How did you calculate the 90 degree angle or the small 30 degree angle ?

Thank you
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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16 Oct 2013, 02:58
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Formula for no. of diagonals in a N sided polygon =

n(n-3)
--------
2
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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26 Dec 2013, 12:24
I think the right answer should be 30(1+2 squareroot3)
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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28 Apr 2015, 05:48
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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27 Jun 2016, 12:00
Hello from the GMAT Club BumpBot!

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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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20 Apr 2017, 05:51
PareshGmat wrote:
Formula for no. of diagonals in a N sided polygon =

n(n-3)
--------
2

Just to clarify:

you mean n(n-3) divided by 2 right?
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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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21 Apr 2017, 09:44
I have a answer but can someone find any flaw in it? Becoz Im not sure if its right or not...

S= side of hexagon
D = diagonal of a regular hexagon

6*S = 30

S=5 ;

Property: The diagonal of a regular hexagon, is twice the side length.

D = 2*S
D = 10;

Regular hexagon has 6 diagonals

6*D is sum of all diagonals

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Re: A regular hexagon has a perimeter of 30 units. What is the [#permalink]

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21 Apr 2017, 09:45
Bunuel wrote:
gmihir wrote:
A regular hexagon has a perimeter of 30 units. What is the sum of the lenghts of all its diagonals ?

Sorry, I can't recall the answer choices but am sure answer 30 is incorrect one.

Look at the diagram below:
Attachment:
Hexagon.png

There are 9 diagonals in a hexagon.

Each of 3 red diagonals equal to $$2*side=2*5=10$$ (since regular hexagon is made of 6 equilateral triangles);
Each of 6 blue diagonals equal to $$2*(side*\frac{\sqrt{3}}{2})=5\sqrt{3}$$ (notice that in 30°, 60°, 90° triangle, where the sides are always in the ratio $$1 : \sqrt{3}: 2$$, half of the blue diagonal is the leg opposite 60°, so it equals to $$side*\frac{\sqrt{3}}{2}$$);

So, the sum of the lenghts of all diagonals is $$3*10+6*5\sqrt{3}=30(1+\sqrt{3})$$.

Hope it's clear.

I have a answer but can someone find any flaw in it? Becoz Im not sure if its right or not...

S= side of hexagon
D = diagonal of a regular hexagon

6*S = 30

S=5 ;

Property: The diagonal of a regular hexagon, is twice the side length.

D = 2*S
D = 10;

Regular hexagon has 6 diagonals

6*D is sum of all diagonals

Re: A regular hexagon has a perimeter of 30 units. What is the   [#permalink] 21 Apr 2017, 09:45
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