Binomial series

[SuperTramp]

What is the range of values that (1-3x)^-¼ is valid for in the binomial expasion

[PJones]

(1-3x)^-¼

if the power is not a positive integer then the expansion is only valid for the x term between -1 and 1
so -1<-3x<1
divide by -3 remember to reverse the inequality when dividing by a negative number.
1/3>x>-1/3
-1/3<x<1/3