3. Sequences
It’s possible to add infinitely many numbers and obtain a
finite sum. For example, the sum ½ + ¼ + 1/8 + 1/16...
represents the accumulated amount of
“taking half of the 1 or ½,
take half of what’s left, or ¼,
then take of half of what’s left or 1/8,
and repeat the process without stopping..”
We see that ½ + ¼ + 1/8 + 1/16 + 1/32... = 1.
..
= 1
7. What is 1/3 + 1/9 + 1/27 + 1/81... = ?
½
¼
1/8
1/16
1/32
(Hint: Let the sum 1/3 + 1/9 + 1/27 + 1/81... = x,
factoring out 1/3 from the left, we’ve
1/3(1 + 1/3 + 1/9 + 1/27 + 1/81...) = x, or
1/3(1 + x) = x, then solve for x.)
8. What is 1/4 + 1/16 + 1/64 + 1/81... = ? (Hint: factor out ¼)
9. What is 1/5 + 1/25 + 1/125 + 1/625... = ? (Hint: factor out 1/5)