Decagon
In geometry, a decagon is a ten-sided polygon or 10-gon.
Regular decagon
A regular decagon has all sides of equal length and each internal angle will always be equal to 144°. Its Schläfli symbol is {10} and can also be constructed as a truncated pentagon, t{5}, a quasiregular decagon alternating two types of edges.
The area of a regular decagon is: (with t = edge length)
An alternative formula is 
where d is the distance between parallel sides, or the height when the decagon stands on one side as base, or the diameter of the decagon's inscribed circle.
By simple trigonometry,
and it can be written algebraically as
Sides
The side of a regular decagon inscribed in a unit circle is 
, where ϕ is the golden ratio, 
.
Construction
As 10 = 2 × 5, a power of two times a Fermat prime, it follows that a regular decagon is constructible using compass and straightedge, or by an edge-bisection of a regular pentagon.
An alternative (but similar) method is as follows:
Podcasts:
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
-
by Teach-in
See The Sun
by: Teach-inSee the sun (See, see the sun)
See the sunshine (See the sun go down)
See the sun (See, see the sun)
See the sunshine (See the sun go down)
As I was younger than today
I liked to dream the clouds away
So I went lonesome down the pave
And left to see the sun go down
I did expect a lonely night
As you came walking by my side
And with the man of my delight
I lived to see the sun go down
Every morning when I wake up
You're out there wherever the feet will go
I pray for giving him back to me
Every day when the things are wrong
I won't be grieving, I will be strong, ohoho
I pray for giving him back to me
But there is a day
You are furling down the day
And you're giving me your hand
It's the end of a nightmare
See the sun (See, see the sun)
See the sunshine (See the sun go down)
See the sun (See, see the sun)
See the sunshine (See the sun go down)
That evening we, you will agree
Enjoyd your coming back to me
And as we walked along the sea
We lived to see the sun go down
Today a man came to my door
He said you won't be back no more
With tears I'm walking along the shore