Discussion
To construct a golden rectangle, begin with a square (ABCD in the diagram) with
sides that measure 1 unit.
Extend one side of the square (red line in the diagram)
Bisect the side of the square that was extended (point E)
Strike an arc with radius DE to intersect the extended side of the square
(point F)
Construct the perpendicular to the extended side at F.
Extend the opposite side of the square to intersect the perpendicular at F.
(point G).
The resulting quadrilateral (ABFG) is a golden rectangle.
The dimensions of the golden rectangle are the measures of AB and BF. But
BF = one half of BC plus EF. But BC = AB, and EF = DE
The measure of DE can be determined by using the Pythagorean Theorem because
DE is the hypotenuse of a right triangle with sides CD measuring 1 and EC
measuring 1/2.
The rectangle that was added to the square is, itself, a golden rectangle
consisting of a square and a rectangle that is a golden rectangle, ad infinitum.
Solution
Let c = the measure of DE, a = the measure of EC, and b = the measure of CD.
a = 1
b = 1/2
Since the measure of DE = the measure of EF and the measure of BE is 1/2,
the measure of BF (the length of the golden rectangle) is or
is roughly 1.62, so the Golden Ratio is approximately 1.62:1