Progression (Sequence and Series)Hard
Question
For the series S = 1 + 
(1 + 2)2 + 
(1 + 2 + 3)2 +
(1 + 2 + 3 + 4)2 +.....
(1 + 2)2 + (1 + 2 + 3)2 +(1 + 2 + 3 + 4)2 +.....Options
A.7th term is 16
B.7th term is 18
C.sum of first 10th terms is
D.sum of first 10th term is
Solution
S = 1 + 
(1 + 2)2 + 
(1 + 2 + 3)2 + 
(1 + 2 + 3 + 4)2 + ....
rth term Tr =
= (1 + 2 ...... + r)2
∴ T7 = 16
ans S10 =
Tr
=
+ (10)(10 + 1) + 10
(1 + 2)2 + (1 + 2 + 3)2 + (1 + 2 + 3 + 4)2 + ....rth term Tr =
= (1 + 2 ...... + r)2∴ T7 = 16
ans S10 =
Tr=
+ (10)(10 + 1) + 10Create a free account to view solution
View Solution FreeMore Progression (Sequence and Series) Questions
If the mean of first n natural numbers is equal to , then n is equal to-...If a,b,c,d are in G.P., then the value of (a − c)2 + (b − c)2 + (b − d)2 − (a − d)2 is-...The mean of first three terms is 14 and mean of next two terms is 18. The mean of all the five terms is-...The value of cot cot-1 is...The sum of three positive numbers constituting an arithmetic progression is 15. If we add 1,4,19 to those numbers respec...