It's hard to see just what you meant. I'll assume you meant
E=√(x(n-x)/(n-1))
Then that gives
E^2 = x(n-x)/(n-1)
(n-1)E^2 = x(n-x)
E^2n - E^2 = xn - x^2
(E^2-x)n = E^2-x^2
n = (E^2-x^2)/(E^2-x)
If I parsed it wrong, maybe you could either (a)
use some parentheses to clear things up, and then
(b) follow similar steps on your own to arrive at the desired result.
Make n the subject of the formula
E=√x(n-x)/n-1
2 answers
A=E^2-x^2/E^2-x