Question

дана арифметическая прогрессия -7 -9 -11 найдите сумму первых семи членов этой прогрессии

Answer 1

(-7)+(-9)+(-11)+(-13)+(-15)+(-17)+(-19)=-91

Answer 2

Arithmetic Progression and Sum of First Seven Terms

The given arithmetic progression is: -7, -9, -11. We need to find the sum of the first seven terms of this progression.

To find the sum of the first seven terms of an arithmetic progression, we can use the formula: Sn = (n/2)(a1 + an), where: - Sn is the sum of the first n terms, - n is the number of terms, - a1 is the first term, and - an is the nth term.

Using the given arithmetic progression, we can calculate the sum of the first seven terms.

The first term (a1) is -7, and the common difference (d) is 2 (since each term decreases by 2).

The formula for the nth term of an arithmetic progression is: an = a1 + (n - 1)d.

Let's calculate the sum of the first seven terms using the formula for the sum of an arithmetic progression.

Sn = (7/2)(-7 + an)

To find an, we can use the formula for the nth term: an = a1 + (n - 1)d.

an = -7 + (7 - 1) * 2 an = -7 + 6 * 2 an = -7 + 12 an = 5

Now we can calculate the sum: Sn = (7/2)(-7 + 5) Sn = (7/2)(-2) Sn = 7*(-1) Sn = -7

So, the sum of the first seven terms of the given arithmetic progression -7, -9, -11 is -7.