Challenge question: If ABCD is a square, and XYZ
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If ABCD is a square, and XYZ is an equilateral triangle, then the area of the square is how many times the area of the triangle?
A) (4√3)/3
B) (8√3)/3
C) 2√6
D) (16√3)/9
E) (16√2)/3
Answer: D
Difficulty level: 650 - 700
Source: www.gmatprepnow.com
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GMAT/MBA Expert
- Brent@GMATPrepNow
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If ∆XYZ is EQUILATERAL, then each angle is 60°Brent@GMATPrepNow wrote:
If ABCD is a square, and XYZ is an equilateral triangle, then the area of the square is how many times the area of the triangle?
A) (4√3)/3
B) (8√3)/3
C) 2√6
D) (16√3)/9
E) (16√2)/3
So, if we draw a line from the center to a vertex, we'll get two 30° angles....
Now drop a line down like this to create a SPECIAL 30-60-90 right triangle
Since the base 30-60-90 right triangle has lengths 1, 2 and √3, let's give the triangle these same measurements...
IMPORTANT: This means the circle's radius = 2, which means the circle's DIAMETER = 4
Notice that the circle's diameter = the length of one side of the square
So, each side of the square has length 4, which means the area of the square = (4)(4) = 16
Okay, now let's determine the area of the triangle
Since we know that one side of the special 30-60-90 right triangle has length √3...
.... we know that the length of one side of the equilateral triangle = 2√3
This allows us to apply a special area formula for equilateral triangles:
Area of equilateral triangle = (√3)(side²)/4
So, the area of ∆XYZ = (√3)(2√3)²/4
= (√3)(12)/4
= 3√3
The area of the square is how many times the area of the triangle?
Answer = 16/3√3
Check the answer choices...not there!
Multiply top and bottom by √3 to get: (16√3)/9
Answer: D
Cheers,
Brent
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The circle is the circumcircle of the triangle, the radius of the circle will be equal to circumradius.
And since it is an equilateral triangle, circumcentre is also the centroid, so the distance between circumcentre and vertex(radius) will be 2/3 of Median(which is the same as altitude).
Length of altitude= sqrt(3)/2*a
So, radius= 2/3* sqrt(3)/2*a
Side of square=2*radius= 2/sqrt(3)*a
Area of square= 4/3*a^2
Area of triangle= sqrt(3)/4*a^2
Ratio= (16√3)/9
And since it is an equilateral triangle, circumcentre is also the centroid, so the distance between circumcentre and vertex(radius) will be 2/3 of Median(which is the same as altitude).
Length of altitude= sqrt(3)/2*a
So, radius= 2/3* sqrt(3)/2*a
Side of square=2*radius= 2/sqrt(3)*a
Area of square= 4/3*a^2
Area of triangle= sqrt(3)/4*a^2
Ratio= (16√3)/9
Let the radius of the circle be x.
The area of the square: $$4x^2$$
Maximum sides of an equilateral triangle in a circle of radius x is: $$x\sqrt{3}$$
Calculate the area of the triangle. Easy straightforward solution.
The correct answer is D. Regards!
The area of the square: $$4x^2$$
Maximum sides of an equilateral triangle in a circle of radius x is: $$x\sqrt{3}$$
Calculate the area of the triangle. Easy straightforward solution.
The correct answer is D. Regards!