Find the second term of an AP if the sum of its first five even terms ...
Since the sum of the first five even terms is 15, we have that the 2nd, 4th, 6th, 8th and 10th term of
the AP should add up to 15. We also need to understand that these 5 terms of the AP would also be
in an AP by themselves and hence, the value of the 6th term (being the middle term of the AP)
would be the average of 15 over 5 terms. Thus, the value of the 6th term is 3. Also, since the sum
of the first three terms of the AP is –3, we get that the 2nd term would have a value of –1. Thus, the
AP can be visualized as:
_, -1, _,_,_,3,….
Thus, it is obvious that the AP would be –2, –1, 0, 1, 2, 3. The second term is –1. Thus, option (c)
is correct.
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Find the second term of an AP if the sum of its first five even terms ...
Given information:
- Sum of first five even terms of an AP = 15
- Sum of first three terms of the same AP = 3
To find: Second term of the AP
Solution:
Let the first term of the AP be 'a' and the common difference be 'd'.
We know that the sum of first five even terms of an AP is given by:
Sum of first five even terms = 2(a+2d) + 2(a+4d) + 2(a+6d) = 6a + 24d
From the given information, we have:
6a + 24d = 15 ---(1)
We also know that the sum of first three terms of the same AP is given by:
Sum of first three terms = a + (a+d) + (a+2d) = 3a + 3d
From the given information, we have:
3a + 3d = 3 ---(2)
Dividing equation (1) by 6, we get:
a + 4d = 5/2
Subtracting equation (2) from the above equation, we get:
d = -1/2
Substituting d = -1/2 in equation (2), we get:
3a - 3/2 = 3
3a = 9/2
a = 3/2
Therefore, the second term of the AP is given by:
a + d = 3/2 - 1/2 = 1
Hence, option (c) is the correct answer.