Chapter 10 - Radical Expressions and Equations - 10-3 Operations with Radial Expressions - Practice and Problem-Solving Exercises - Page 618: 61

$(1+\sqrt 5)*n/2 - n $

The golden ratio is $(1+\sqrt 5)/2$. This is a ratio of length to width. Let width = $n$ and let $x$ be the amount needed to make the golden rectangle. $(1+\sqrt 5)/2 = $(x+n)/n$ $(1+\sqrt 5)*n/2 = x+n$ $(1+\sqrt 5)*n/2 - n = x$