Can someone help me?
2 answers:
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Looks like you just evaluated the summand for the given value of 
, whereas the question is asking you to find the value of the sum for the first terms.
Let
. Then 
is the 
th partial sum.
happens to be the first term in the series, which is why that box is marked correct:
But the next partial sum is not correct:
and this is not the same notion as the second term (which indeed is 0.75) in the series.
Let
But the next partial sum is not correct:
and this is not the same notion as the second term (which indeed is 0.75) in the series.