Painting A Hexagram

Geometry Level 1

The above figure shows a regular hexagram inscribed in a circle of radius 10 units. Find the area of the shaded region (in unit 2 \text{unit}^2 ).

Round your answer to the nearest integer.

47 64 56 34

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

Ahmad Saad
Mar 1, 2016

O A = R = 10 units , A P = 1 2 A O = 5 units , P B = 5 3 units Area of triangle A B C = 1 2 5 5 3 = 25 3 unit 2 \begin{aligned} && OA = R = 10 \text{ units} , AP = \dfrac12 AO = 5 \text{ units} , PB = \dfrac5{\sqrt3} \text{ units} \\ && \Rightarrow \text{Area of triangle } ABC = \dfrac12 \cdot 5 \cdot \dfrac5{\sqrt3} = \dfrac{25}{\sqrt3} \text{ unit}^2 \end{aligned}

Area of the regular hexagram is 12 25 3 = 100 3 12 \cdot \dfrac{25}{\sqrt3} = 100\sqrt3 .

Area of the circle is π R 2 = π 1 0 2 = 100 π \pi R^2 = \pi \cdot 10^2 = 100 \pi .

Thus the area of the shaded region is 1 3 ( 100 π 100 3 ) = 46.984 47 unit 2 \dfrac13 ( 100\pi - 100\sqrt3) = 46.984\ldots \approx 47 \text{ unit}^2 .

Superb Ahmad! Great effort! :)

Onkar Shirodkar - 5 years, 3 months ago

Log in to reply

Many Thanks.

Ahmad Saad - 5 years, 3 months ago
Elvin Ding
Mar 12, 2016

Great work Elvin! :)

Onkar Shirodkar - 5 years, 3 months ago

Log in to reply

Thank you!

Elvin Ding - 5 years, 3 months ago
Onkar Shirodkar
Feb 29, 2016

Radius of circle= 10 units
Altitude of an equilateral triangle is divided in the ratio= 2:1 at the center of the circle
Hence the altitude of the equilateral triangle= 10 * (2+1)/2 = 15 units
Altitude of equilateral triangle= Sqrt 3* side/2
Hence, we get side bigger triangle.
Side of each smaller triangle= side of big triangle/3
There are 12 such small triangles (6 external and 6 within the hexagon).
Find the area of each smaller triangle and multiply it by 12.
Subtract this area from the area of the circle.
The value that you get it the value of segments.
Divide it by 3 to get the value of 2 segments (which is the shaded portion).
The area comes out to be 47 unit2.



0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...