Could not understand the solution of this problem

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The hexagon ABCDEF is regular.That means all its sides are the same length and all its interior angles are the same size.Each side of the Hexagon is 2 feet.What is the area of the rectangle BCEF ?The answer is 4(square root of 3)

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The solution given in the book is that Given BC and EF are each 2 feet.Since area of the rectangle is length times width ,you must find the length(CE or BF).Look at Triangle ABF .It has two equal sides(AB=AF) ,So the perpendicular from A to the line BF divides ABF into two congruent right triangles AHF and AHB each with hypotenuse 2.

The angle FAB is 120 since the total of the angles of the hexagon is 720 .So each of the two triangles is 30-60-90 right triangle with hypotenuse 2.So AH=1,anf FH=HB =Square root of 3.There for BF=2*^3 and the area is 2*2^3=4^3 square feet.

I did not understand how they arrived at AH=1 from the angles of the triangles and hypotenuse?If anyone can pls explain to me.Thanks[/img]
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by Mom4MBA » Tue Feb 02, 2010 2:04 pm
I hope u got that the angles of triangle AHB are B=30º, A=60º, H=90º

so now going by 30:60:90 rule we get that the ratio of lines in front of these angles is 1:√3: 2
given AB = 2 ; AH will be 1 and HB=√3

for the rectangle one side is 2 the other one will be √3+√3=2√3

area = 2 x 2√3 = 4√3

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by ajith » Wed Feb 03, 2010 3:34 am
manjus_mailme wrote:The hexagon ABCDEF is regular.That means all its sides are the same length and all its interior angles are the same size.Each side of the Hexagon is 2 feet.What is the area of the rectangle BCEF ?The answer is 4(square root of 3)

I did not understand how they arrived at AH=1 from the angles of the triangles and hypotenuse?If anyone can pls explain to me.Thanks[/img]
in the triangle FAB, angle FAB = 120; Angle AFB = Angle ABF =30 Degree

Which makes Triangle AHB a 30-60-90 triangle with angle ABH = 30 Degree

Now the sides of the 30-60-90 triangle are in 1:sqrt(3):2 ration

So AH/AB = 1/2 => AH =1
BH/AB = sqrt(3)/2 => BH = Sqrt(3)
FB = 2BH = 2*sqrt(3)
Area of the rectangle BCEF = EF*FB = 2*2*sqrt(3) = 4sqrt(3)
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by manjus_mailme » Wed Feb 03, 2010 6:52 am
Thanks a lot for the reply.Now I got it.

Manju

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by money9111 » Wed Feb 03, 2010 9:08 am
what would be wrong with saying that Triangle ABF is an isoceles triangle with sides 2 & 2 thus making the 3rd side xsqrt2.

Now as I just typed that I realized why that is incorrect, but I decided to post my reasoning so you guys can confirm.

Even though yes having two sides equal to 2 means that it is isoceles.. it is in fact not a 45 ,45, 90 triangle so you cannot use x, x, xsqrt2.
Last edited by money9111 on Wed Feb 03, 2010 9:52 am, edited 1 time in total.
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by ajith » Wed Feb 03, 2010 9:16 am
money9111 wrote:what would be wrong with saying that Triangle ABF is an isoceles triangle with sides 2 & 2 thus making the 3rd side xsqrt2.

Now as I just typed that I realized why that is incorrect, but I decided to post my reasoning so you guys can confirm.

Even though yes having two sides equal to 2 means that it it's isoceles.. it is in face not a 45 ,45, 90 triangle so you cannot use x, x, xsqrt2.
It is not a 45-45-90 triangle instead it is 30-30-120 triangle, yes that is the mistake
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by Mom4MBA » Wed Feb 03, 2010 9:34 am
It is not a 45-45-90 triangle instead it is 30-30-120 triangle, yes that is the mistake
Hey that's what I was going to say 1:1:√2 goes for 45:45:90 triangle, but thanks for the post because for a moment you confused me and I had to pick up my notes to check.

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by money9111 » Wed Feb 03, 2010 9:54 am
i get so trigger happy when I see an isoceles triangle that i'm like "YES... I CAN DO THIS... 1-1-SQRT2" LOL i want to apply that to everything! now watch on the actual GMAT i won't get any of these questions because I like them so much :-/ ... ok back to divisibility and primes and consecutive integers = (my weakness) ;-)
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by Mom4MBA » Wed Feb 03, 2010 1:57 pm
This is a good and easy link to understand the rule.

https://www.themathpage.com/aTrig/30-60- ... .htm#proof

good luck :)
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