Science:Math Exam Resources/Courses/MATH105/April 2015/Question 01 (l)/Hint 1

Observe that

$\sum _{k=n}^{\infty }a_{k}=\sum _{k=0}^{\infty }a_{k}-\sum _{k=0}^{n-1}a_{k}$

to separate the series into two series you can calculate: an infinite geometric series and a finite geometric series.