Question

А15=11S15=105a1=?d=?

Answer 1

A₁₅=11    S₁₅=105     a₁-?     d-?
a₁₅=a₁+14d=11
S₁₅=(a₁+a₁₅)*15/2=105
(a₁+11)*15/2=105  |×(2/15)
a₁+11=14
a₁=3
3+14d=11
14d=8  |÷14
d=4/7.
Ответ: a₁=3       d=4/7.

Answer 2

$105= \frac{a_1+11}{2} \cdot 15 \\ 7 = \frac{a_1+11}{2} \\ 14=a_1+11 \\ a_1=14-11 \\ a_1 = 3 \\ d = \frac{11-3}{15-1} = \frac{8}{14} = \frac{4}{7}$

Answer 3

It looks like you've provided a series of equations with some missing values. Let's try to solve them step by step:

1. A15 = 11
2. S15 = 105

We can't deduce the values of "a1" and "d" without additional information. The given equations only provide the 15th term of an arithmetic sequence (A15) and the sum of the first 15 terms (S15).

An arithmetic sequence is a sequence of numbers in which the difference between any two consecutive terms is constant. The formula for the nth term of an arithmetic sequence is:

An = a1 + (n-1) * d

Where: An = the nth term a1 = the first term d = the common difference between consecutive terms n = the term number

Since we don't have enough information, we can't determine the values of "a1" and "d" from the given equations. If you have more equations or additional information, please provide them, and I'll be happy to assist you further in solving the problem.