Question

21+24+27+...+63 хелп плиз​

Answer 1

Это можно рассчитать по формуле суммы арифметического ряда:

S_n = n/2 * (a_1 + a_n)

Где n — количество терминов, a_1 — первый термин (в данном случае 21), а a_n — n-й термин (в данном случае 63).

Подставляем значения:

п = (63 - 21) / 6 + 1 = 7

а_1 = 21

а_п = 63

С_н = 7/2 * (21 + 63) = 7/2 * 84 = 294

Таким образом, сумма ряда 21 + 24 + 27 + ... + 63 равна 294.

Answer 2

To find the sum of an arithmetic series, you can use the formula:

S = (n/2)(a + l)

where: S is the sum of the series, n is the number of terms, a is the first term, and l is the last term.

In this case, the first term is 21, and the last term is 63. The common difference between the terms is 3 (27 - 24 = 3).

To find the number of terms, you can use the formula for the nth term of an arithmetic series:

l = a + (n-1)d

Rearranging this formula, we get:

n = (l - a) / d + 1

Now, let's calculate the sum of the series:

a = 21 l = 63 d = 3

n = (63 - 21) / 3 + 1 n = 42 / 3 + 1 n = 14 + 1 n = 15

Using the formula for the sum of an arithmetic series:

S = (n/2)(a + l) S = (15/2)(21 + 63) S = (15/2)(84) S = 7(84) S = 588

Therefore, the sum of the series 21 + 24 + 27 + ... + 63 is 588.