# Math

The sum of the first 21 terms of a linear sequence is 28 and the sum of the first 28 terms is 21 . find which term of the sequence is 0 and also the sum of the terms preceeding it

1. 👍 0
2. 👎 0
3. 👁 528
"The sum of the first 21 terms of a linear sequence is 28"
---> (21/2)(2a + 20d) = 28
2a + 20d = 8/3

"the sum of the first 28 terms is 21"
---> (28/2)(2a + 27d) = 21
2a + 27d = 3/2

subtract them
7d = -7/6
d = -1/6
2a + 20(-1/6) = 8/3
2a = 6
a = 3

term(n) = 3 + (n-1)(-1/6)
= 3 - n/6 + 1/6
= (18 - n + 1)/6 = (19 - n)/6

so you want (19-n)/6 = 0
19 = n

so the 19th term is 0

now find sum(18)

1. 👍 0
2. 👎 1
👨‍🏫
Reiny
2. Itâ€™s complicated and complex

1. 👍 0
2. 👎 0

## Similar Questions

1. ### Math

Question 1 Write the first four terms of the sequence whose general term is given. an = 3n - 1 Answer 2, 3, 4, 5 2, 5, 8, 11 -2, -5, -8, -11 4, 7, 10, 13 3 points Question 2 Write the first four terms of the sequence whose general

2. ### math

5. In a geometric sequence, the sum of the first five terms is 44 and the sum of the next five terms is -11/8. Find the common ratio and first term of the series.

3. ### Maths

The sum of 1st five terms of an AP nd the sum of the 1st seven termd of the same AP is 167. If the sum of the 1st ten terms of this AP is 235, find the sum of its1st twenty terms

4. ### maths

the sum of the 4th and 6th terms of an A.P is 42. the sum of the 3rd and 9th terms of the progression is 52. find the first term, the common difference and the sum of the first ten terms of the progression.

1. ### maths

the sum of the first nine terms of an arithmetic sequence 216. The 1st, 3rd and 7th terms form the first three terms of a geometric sequence therefore find the common difference

Question 1 Write the first four terms of the sequence whose general term is given. an = 3n - 1 Answer 2, 3, 4, 5 2, 5, 8, 11 -2, -5, -8, -11 4, 7, 10, 13 3 points Question 2 Write the first four terms of the sequence whose general

3. ### Maths

The 5th,9th and 16th terms of a linear sequence A.P are consecutive terms of an exponential sequence.Find the common difference of the linear sequence in terms of the first term.

4. ### Math

an = 3n - 1 Answer 2, 3, 4, 5 2, 5, 8, 11 -2, -5, -8, -11 4, 7, 10, 13 3 points Question 2 Write the first four terms of the sequence whose general term is given. an = 2(2n - 3) Answer -6, -2, 2, 6 -1, 1, 3, 5 -2, -4, -6, -8 -2,

1. ### math

The first and second terms of an exponential sequence (G.P) are respectively the first and third terms of a linear sequence (A.P). The fourth term of the linear sequence is 10 and sum of its first five terms is 60. find (a) the

2. ### Can someone help me?!

The 1st, 5th and 13th terms of an arithmetic sequence are the first three terms of a geometric sequence with a common ratio 2. If the 21st term of the arithmetic sequence is 72, calculate the sum of the first 10 terms of the

3. ### Math

The sum of first four terms of a linear sequence is 26 and that of the next four terms is 74.find the value of the first term and the common difference

4. ### maths

In an arithmatic sequence, sum of 9 terms is 279 and sum of 20 terms is 1280. Find 5th term ? Find 16th term ? Write the sequence.