Question 199680
The series


*[Tex \LARGE \displaystyle \sum_{k=1}^\infty a r^{k-1}]



will converge if and only if *[Tex \LARGE \left|r\right|<1]



So this means that you simply need to solve {{{abs(x-2)<1}}} to find the set of x values (since in this case, {{{r=x-2}}})