solve function

I think you need to relearn functions. A function is therefore a many-to-one (or sometimes one-to-one) relation. The set of values at which a function is defined is called its domain, while the set of values that the function can produce is called its range. mathworld.wolfram.com/Function.html

The binomial expansion of this is :

-729 x^3+1701 x^2-1323 x+343