Find the complete set of values of a such that `(x^2-x)//(1-a x)` attains all real values.

Explanation

`y=(x^(2)-x)/(1-ax)`
or ` x^(2)-x=y-axy`
or `x^(2)+x(ay-1)-y=0`
Since x is real we get
`(ay-1)^(2)+4y ge 0`
or ` a^(2)y^(2)+2y(2-a)+1 ge 0 AA y in R`
So, as `a^(2) gt 0`,
`4(2-a)^(2)-4a^(2) le 0`
or ` 4-4a le 0`
or ` a in [1, oo)`