# arithmetic progression

posted by .

If sum of first 21 terms of an arithmetic progression is 13 and that of first 13 terms is 21, show that sum of first 34 terms is -34 ?

• arithmetic progression -

use the first two facts to find d,a1

Sn=n/2(2a1+(n-1)d)

you will have two unknowns, two equations.

then, find s34

## Similar Questions

1. ### arithmetic

Two arithmetic progression have thd same first and last terms.the first arithmetic progression has 21 terms with a common difference of 9.How many terms has the other arithmetic progression if its common difference is 4?
2. ### algebra 2

An arithmetic progression has 5 terms that have a sum of 200. The sum of the last three terms added to 6 times the sum of the first two terms equals zero. What is the first term?
3. ### maths

1) The first term of arithmetic progression is -20 and the sum of it's term is 250. find it's last term if the number of it's terms is 10 2) Find the fifth term from the arithmetic progression -12, -9, -6 hence find the sum of it's …
4. ### Maths

1..The first 2 terms of a geometric progression are the same as the first two terms of an arithmetic progression.The first term is 12 and is greater than the second term.The sum of the first 3 terms od the arithmetic progression is …
5. ### math

The first, the third and the seventh terms of an increasing arithmetic progression are three consecutive terms of a geometric progression. In the first term of the arithmetic progression is 10 find the common difference of the arithmetic …
6. ### algebra

if 1, 2, 7 and 20, respectively, are added to the first terms of an arithmetic progression, a geometric progression of four terms is obtained. find the first term and common difference of the arithmetic progression the answers are …
7. ### math

An arithmetic progression as the same first and second terms as the geometric progression. Find the sum of the first 20 terms of the arithmetic progression. How do I do this?
8. ### math C2 sequences and series

The eight,fourth and second terms of an arithmetic progression form the first three terms of a geometric series. The arithmetic progression has first term A and common difference d, and the geometric progression has first term G and …
9. ### Math

In a particular arithmetic progression, the sum of the first 10 terms is equal to the sum of the first twenty terms. Show that the sum of the first 30 terms is equal to 0.
10. ### arithmetic progression

An arithmetic progression has 3 as its first term. Also, the sum of the first 8 terms is twice the sum of the first 5 terms. Find the common difference.

More Similar Questions