I am reading Stillwell's Elements of Algebra, he gives this figure:
$\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad$
And then:
What is this easy application of the Pythagorean theorem? I have tried to measure it with coordinates in the following way:
$\quad\quad\quad\quad\quad\quad\quad\quad\quad\quad$
And then taking $d((0,0,\frac{T}{2}),({\frac{1}{2}},\frac{T-1}{2},0))$ which gives me $1$ when I substitute $T$ for $\frac{1+\sqrt{5}}{2}$ as expected. But I suspect he wanted something quite simpler.