How much pure water must be mixed with 10 liters of a 25% acud solution to reduce it to a 10% acid solution
1 answer:
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Answer:
This series is convergent. The partial sums of this series converge to .
Step-by-step explanation:
The th partial sum of a series is the sum of its first
terms. In symbols, if
denote the
th term of the original series, the
th partial sum of this series would be:
.
A series is convergent if the limit of its partial sums, , exists (should be a finite number.)
In this question, the th term of this original series is:
.
The first thing to notice is the in the expression for the
th term of this series. Because of this expression, signs of consecutive terms of this series would alternate between positive and negative. This series is considered an alternating series.
One useful property of alternating series is that it would be relatively easy to find out if the series is convergent (in other words, whether exists.)
If is an alternating series (signs of consecutive terms alternate,) it would be convergent (that is: the partial sum limit
exists) as long as
.
For the alternating series in this question, indeed:
.
Therefore, this series is indeed convergent. However, this conclusion doesn't give the exact value of . The exact value of that limit needs to be found in other ways.
Notice that is a geometric series with the first term is
while the common ratio is
. Apply the formula for the sum of geometric series to find an expression for
:
.
Evaluate the limit :
.
Therefore, the partial sum of this series converges to .