in a sequence of 21 terms the first 11 terms are u in ap with common d...
The middle term of the AP is the 6th term, therefore,
6th term= a+(6-1)d= a+10
The middle term of the GP is the 6th term,
6th term = A(2)^5= 32A
Hence= 32A = a+10 (1)
The first term of GP=11th term of AP, therefore
A= a+10*2=a+20 (2)
From 1 and 2,
a= -630/31
From (2), A= a+20 therefore A= -10/31
As the middle term of the sequence is the first term of the GP,
Hence answer is -10/31
in a sequence of 21 terms the first 11 terms are u in ap with common d...
Explanation:
Understanding the Given Conditions:
- We are given a sequence of 21 terms, with the first 11 terms forming an arithmetic progression (AP) with a common difference of 2.
- The last 11 terms form a geometric progression (GP) with a common ratio of 2.
- The middle term of the AP is equal to the right middle term of the GP.
Finding the Middle Term of the AP:
- Since the first term of the AP is u, the middle term can be calculated using the formula for the middle term of an AP:
Middle term of AP = u + (n/2 - 1) * d, where n is the total number of terms and d is the common difference.
- In this case, n = 11 and d = 2, so the middle term of the AP is u + 10 * 2 = u + 20.
Finding the Right Middle Term of the GP:
- The right middle term of a GP can be calculated using the formula:
Right middle term of GP = a * r^(n/2 - 1), where a is the first term of the GP, r is the common ratio, and n is the total number of terms.
- In this case, a is the 11th term of the sequence, which can be calculated as u + 10 * 2 = u + 20.
- Therefore, the right middle term of the GP is (u + 20) * 2^(11/2 - 1) = (u + 20) * 2^5 = (u + 20) * 32 = 32u + 640.
Finding the Middle Term of the Entire Sequence:
- Since the middle term of the AP is u + 20 and the right middle term of the GP is 32u + 640, we can set them equal to each other:
u + 20 = 32u + 640
Solving this equation will give us the value of u, which can then be used to find the middle term of the entire sequence.