Quote:
Originally Posted by Bob Silverman
a^3 + b^3 = 20
ab = 2
x = 2
x^3 = (a+b)^3 = 8
I'm not sure what else you are looking for.

The problem is with the third line (x = 2). I wanted to simplify cbr(10 + sqrt(108)) + cbr(10  sqrt(108)) without knowing a priori that the answer is 2.
That way, it would be possible to generalize the technique to cases where I don't know what x equals to beforehand.