Let , denote the sum of the infinite geometric series whose first term is and the common ratio is . Then the value of is
Answer: 3
Solution
The sum of an infinite geometric series with first term and common ratio (where ) is .
For :
Now:
This is a telescoping series:
Adding (which is negligible), the answer is 3.
For :
Now:
This is a telescoping series:
Adding (which is negligible), the answer is 3.
JEE Advanced · 2010 · 11 Apr 2010 · Paper 1 · Integer answer