well, by using basic trigonometry

first, consider the golden ratio, otherwise known as the divine proportion (1.6180339887...)

now, let's punch these numbers into a calculator and use the sin and cos functions:

sin (666˚) = -0.80901699437
cos ([6x6x6]˚) = cos (216˚) = -0.80901699437

and if we add these two numbers together, the result is: -1.6180339887...

making it the additive inverse of the Golden Ratio.

pretty cool right?