If you do as mentioned, "take the length from the tower to the guy and
double it", you'll be off by a factor of 3^(1/2)/2 or about .87. Remember
your HS trig and the relationship of the sides of a 30-60-90 triangle. Then
you have to orient the triangle correctly on your plans. The hypotenuse is
the distance from the tower to the guy anchor, the long leg is half the
distance from guy anchor to guy anchor.
The relationship of the triangle is hypotenuse = 1
short leg = 1/2
long leg =
3^(1/2)/2 or about .87
for example, if the distance from the tower to the guy anchor is 50ft. The
distance from anchor to anchor will be
(2)(.87)(50)ft. + 85ft.
This result is very different from 2 x 50ft = 100ft.
Given the tolerance levels needed here, Steve's method probably is the easiest.
Given that I'm a HS math teacher and am in math grad school. It's a bit
easier for me to remember my HS trig.