the golden ratio
| is the irrational constant |
|
1.6180...[3] |
a and b (where a > b) are in the golden ratio if:
(a+b)/a = a/b.[3]
...it follows that a rectangle whose
sides are in the golden ratio...
the golden ratio
...it follows that a rectangle whosesides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...it follows that a rectangle whose
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over...
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over...
...it follows that a rectangle whose
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over...
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over...
...it follows that a rectangle whose
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over... and over...
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over... and over...
...it follows that a rectangle whose
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over... and over...
and over...
sides are in the golden ratio...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over... and over...
and over...
...can have a square cut out of it,
and the remaining rectangle is golden...
...over... and over... and over...
and over... and over
and the remaining rectangle is golden...
...over... and over... and over...
and over... and over
...over... and over... and over...
and over... and over... and over...
and over... and over... and over...
...infinitely.
so what?
so what?
- it's cool.
so what?
- it's cool.
-
the ratio shows up in the construction of a regular pentagon.[4] This is how the Greeks discovered it.
Proof:1. 
Fact: If you take a regular pentagon, and draw diagonals from one vertex to the two non-adjacent vertices, you end up trisecting the angle corresponding to the vertex you drew the diagonals from. 2. 
Using the fact in (1) we see that angle CAD ~ angle EAD ~ angle BDA ~ angle EDA. Then triangle FDA and triangle EDA share two pairs of congruent angles and side AD. Therefore, triangle FDA = triangle EDA (by Angle-Side-Angle). It follows that side AF = side DF = 1. 3. Using the fact in (1) and since angle BFC ~ angle AFD (vertical angles), we see that triangle ADF and triangle BCF are similar.
So 
, but 
.
Thus 
, 
, so 
.
Solving this quadratic equation gives us one positive value for x (distances must be positive):

, and so y is our golden ratio.
so what?
- it's cool.
- the ratio shows up in the construction of a regular pentagon.[4] This is how the Greeks discovered it.
- the ratio is culturally important in art and design
- some say the ratio shows up everywhere in nature.[2]
- but what the hell does this have to do with Fibonacci Numbers?
next section: the connection »

