The 'divina proporzione' or golden ratio, represented by the Greek letter phi, is derived from the equation below where $a$ and $b$ are parts of a line.
 $a+b:a=a:b$ i.e. $\frac{a+b}{a}=\frac{a}{b}=\Phi\ \quad$(phi)
If $b = 1$ show that $\Phi = a = (\sqrt 5 + 1 )/2 = 1.618034...$.
In the following equation what does $x$ equal?