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In the figure, each side of square ABCD has length 1, the

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Senior Manager
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In the figure, each side of square ABCD has length 1, the [#permalink]  25 Jan 2010, 09:05
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In the figure, each side of square ABCD has length 1, the length of line Segment CE is 1, and the length of line segment BE is equal to the length Of line segment DE. What is the area of the triangular region BCE?

A.. 1/3
B. (2^-2 )/4
C. 1/2
D. (2^-2)/2
E. 3/4
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Re: Set 25 [#permalink]  25 Jan 2010, 13:24
If someone can explain this, that'll be great. I keep on getting (rad 2) over 4, which is not any of the answers.
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Re: Set 25 [#permalink]  26 Jan 2010, 02:43
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In the figure, each side of square ABCD has length 1, the length of line Segment CE is 1, and the length of line segment BE is equal to the length of line segment DE. What is the area of the triangular region BCE?

This proble can be solved in many ways. One of the approaches:

Note that as BE=DE the triangles BCE and CDE are congruent (all three sides are equal) --> \angle{BCE}=\angle{DCE}. So if we continue the line segment CE it will meet with the crosspoint of the diagonals, let's call it point O. Also note that EO will be perpendicular to BD, as diagonals in square make a right angle.

The area BCE=BOE-BOC.

Area of BOC is one fourth of the square's =\frac{1}{4}.

Area BOE, \frac{1}{2}BO*EO. BO=\frac{\sqrt{2}}{2}, half of the diagonal of a square. EO=CE+CO=1+\frac{\sqrt{2}}{2}=\frac{2+\sqrt{2}}{2}, CO is also half of the diagonal of a square.
So AreaBOE=\frac{1}{2}BO*EO=\frac{1}{2}*\frac{\sqrt{2}}{2}*\frac{2+\sqrt{2}}{2}=\frac{\sqrt{2}+1}{4}.

Area BCE=BOE-BOC=\frac{\sqrt{2}+1}{4}-\frac{1}{4}=\frac{\sqrt{2}}{4}

None of the answer choices shown is correct.
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Kudos [?]: 931 [0], given: 235

Re: Set 25 [#permalink]  26 Jan 2010, 06:39
IMO

Take Angle CBE = BEC = CED = CDE = x
Take Angle BCE = DCE = y

Now 2x+y = 180 in triangle BCE.

Also angle BCD + 2y = 360 => 2y= 360-90 = 270
=> y = 135
=> x= (180-135)/2 = 45/2

in triangle BCE , draw a perpendicular to base BE which meets BE at Z

Now in Triangle BCZ , BC = 1
Angle EBC = 45/2

=> BZ = cos(45/2)
CZ = sin(45/2)

Area of triangle BCE = \frac{1}{2}* BE * CZ
= \frac{1}{2}* 2*cos(45/2) * Sin(45/2)
=\frac{1}{2}* sin45 using -> sin(2A) = 2 * SinA * cosA
=\frac{1}{2\sqrt{2}}

which should be 2^ (-3/2)

I think you have wrongly written your ans.. Please check if D is 2^ (-3/2)
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Kudos [?]: 38 [0], given: 11

Re: Set 25 [#permalink]  26 Jan 2010, 07:39
CE bisects angle BCD, therefore angle ACB=45

A(BCE)=1/2(BC*CE*sin(ACB)=1/2*1*1*sqrt2/2=sqrt2/4
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Re: Set 25 [#permalink]  28 Jan 2010, 12:38
Basically adding a picture for more clarity... original one is throwing bit off...!
OB=OC=(sq. rt 2)/2
rest is simplification... agree with the answers above of sqrt2/4.
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Re: Set 25   [#permalink] 28 Jan 2010, 12:38
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