Circles Inscribed In A Rectangle

Geometry Level 3

As shown above, six circles are inscribed in one rectangle. They all have equal radii, and the total area of the circles is 2 π 2\pi Find the area of the rectangle.


The answer is 8.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

3 solutions

Aidan Poor
Jun 15, 2018

To begin solving this problem, notice that the length and height of the rectangle can be written in terms of the radius, r r , of the circles as such:

L e n g t h = 6 r Length=6r

H e i g h t = 4 r Height=4r

Now to solve for the area of the rectangle, solving for the radius is prominent. As said in the given, the combined area of all the circles is 2 π 2\pi . Using this information, we can solve for the area of one circle as such:

Let x x = area of one circle.

6 x = 2 π \therefore 6x=2\pi \Rightarrow 3 x = π 3x=\pi \Rightarrow x = π 3 \boxed{x=\frac{\pi}{3}}

Now that we have solved for the area of one circle, we can solve for the radius by setting it equal to the formula for finding the area of a circle as such:

π 3 = π r 2 \frac{\pi}{3}=\pi r^{2} \Rightarrow 1 3 = r 2 \frac {1}{3}=r^{2} \Rightarrow r = 1 3 \boxed{r=\frac{1}{\sqrt{3}}}

Now that we know the value of the radius, r r , we can reliably solve for the area of the rectangle as such:

L e n g t h = 6 × 1 3 Length=6 \times \frac{1}{\sqrt{3}} \Rightarrow L e n g t h = 6 3 Length=\frac{6}{\sqrt{3}}

H e i g h t = 4 × 1 3 Height=4 \times \frac{1}{\sqrt{3}} \Rightarrow H e i g h t = 4 3 Height=\frac{4}{\sqrt{3}}

\therefore Area of the Rectangle = 6 3 × 4 3 \frac{6}{\sqrt{3}} \times {\frac{4}{\sqrt{3}}} \Rightarrow 24 3 \frac{24}{3} \Rightarrow 8 \boxed{8}

Ram Mohith
Jun 15, 2018

Let the radius of each circle be r r d i a m e t e r = 2 × r \implies diameter = 2 \times r

Now, length of the rectangle is combination of diameters of 3 equal circles and breadth of the rectangle is the combination of diameters of 2 equal circles.

l = 3 × 2 r = 6 r \implies l = 3 \times 2r = 6r

b = 2 × 2 r = 4 r \implies b = 2 \times 2r = 4r

Now, area of 6 equal circles is 2 π .

6 × 2 π r 2 = 2 π 6 \times 2πr^2 = 2π

r 2 = 1 3 \implies r^2 = \dfrac{1}{3}

Now, area of the rectangle = l × b l \times b

6 r × 4 r = 24 r 2 = 24 × 1 3 = 8 \implies 6r \times 4r = 24r^2 = 24 \times \dfrac{1}{3} = 8

Therefore, area of the rectangle is 8 . \color{#20A900}\text{area of the rectangle is 8 .}

Blan Morrison
Jun 15, 2018

Let r r be the radius of one of the gray circles.

Since the total area of all the circles combined is 2 π 2\pi , that means 6 π r 2 = 2 π 6\pi r^2=2\pi r 2 = 1 3 \implies r^2=\frac{1}{3} r = 1 3 \implies r=\frac{1}{\sqrt{3}}

Because the circles are inscribed in the rectangle, that means the dimensions of the rectangle are 6 r × 4 r 6r \times 4r :

6 3 × 4 3 = 24 3 = 8 \frac{6}{\sqrt{3}} \times \frac{4}{\sqrt{3}} = \frac{24}{3} = \boxed{8}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...