5. Subtract the sum of
-11
- 2 and 3
-8
5
from the sum of
and
3
2
12
2
if that
T
-
-
Answers
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MATHS
Let sum of n terms of a series be n(2n−1). Find its mth terms
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ANSWER
Let S
m
and S
m−1
denote the sum of the first m and (m-1) terms respectively.
S
m
=T
1
+T
2
+T
3
+......+T
m−1
+T
m
S
m
=T
1
+T
2
+T
3
+.....+T
m−1
Subtracting
S
m
−S
m−1
=T
m
⇒T
m
=(m(2m−1))−(m−1)(2(m−1)−1))
=(2m
3
−m)−(2m
2
−5m+3)
=4m−3
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0
Sorry I don't know the answer sorry once again dear
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