Find the power series representation of:
f(x) = x/9-x^2
factor out x/9 and we get:
1/(1-x^2/9) or 1/(1-(x/3)^2)
Now my question is. The solution shows that we use the geometric series representation, 1/1-r. In this case, shouldn't r be x^2/9. The solution uses x/3.