The figure to the right shows an irregular hexagon with six circles of radius 1, where the hexagon's vertices are the circles' centers.
Find the sum of the areas of the black regions.
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.
That's nice, I love creativity +1
Nice! how do we prove this?
I am in love with this solution. +1
As the circles have equal radius, the black sectors can be joined to make circles. A circle is completed by 3 6 0 ° so firstable calculate the sum of angles of a hexagon as follows:
1 8 0 ° × 6 − 3 6 0 ° = 7 2 0 °
With 7 2 0 ° can be maked to circles so black area = 2 × π × 1 × 1 = 2 π
I gave up because I typed in 2pi and couldn't figure out what to do. Maybe you could add "to the nearest millionth?"
I wrote 6,28, it said "The answer must be a decimal number". Isn't 6,28 a decimal number?
Log in to reply
no 6,28 isn't a decimal no. but 6.28 is :P
Using decimal, this would be 6.28 :)
@Domenico Franceschelli Did you wrote 6,28 or 6.28? If you wrote the first one, your answer was probably not accepted as a valid one.
Log in to reply
Then it was my fault: I wrote 6,28 instead of 6.28. In Italy we use commas as decimal marks :)
Log in to reply
@Domenico Franceschelli – I hear you loud and clear. In Serbia is the same. Luckily I am into programming, so I know that for type double or float dots are used instead of commas. :)
Ok to be more precise. No one knows what should be used here, but I usually use comas.
The sum of the interior angles is 7 2 0 ∘ . One circle is 3 6 0 ∘ . So we need to find the area of 3 6 0 7 2 0 = 2 circles. We have
A = 2 ( π ) ( 1 2 ) ≈ 6 . 2 8 3 1 8 5 3 0 7
This is how I did it.
I figured that the black area could fit in to 2 black circles. From there I just found the area of one circle (1 x 1 x 3.14) and multiplied it by 2. Therefore, the answer would be 3.14 x 2: 6.28
I assumed an arbitrary shape, took the top and bottom circles to infinity, and only the larger areas remain, all black, giving 2 pi.
The sum of all n-irregular angles can be determined by ( n − 2 ) 1 8 0 . The sum of all angles of the hexagon is ( 6 − 2 ) 1 8 0 = 4 ⋅ 1 8 0 = 7 2 0 .
So, the shaded area is 3 6 0 7 2 0 ⋅ 1 2 π = 2 π ≈ 6 . 2 8 .
Problem Loading...
Note Loading...
Set Loading...
what about converting the general case into a standard one :D
Then we have θ = 9 0 × 4 + 1 8 0 × 2 = 7 2 0 = 2 c i r c l e s 2 × A r e a ( c i r c l e ) = 4 × π × r 2 = 2 π = 6 . 2 8