Question

A1=6,4 d=0,8 S9=?арифметическая прогрессия

Answer 1

$a_1=6.4 \\ d=0.8 \\ n=9 \\ S_n=\frac{a_1+a_n}{2}*n= \frac{a_1+a_1+(n-1)*d}{2}*n=\frac{2a_1+(n-1)*d}{2}*n \\ S_9=\frac{2*6.4+(9-1)*0.8}{2}*9=(6.4+4*0.8)*9=86.4$

Answer 2

It seems like you're dealing with an arithmetic progression where the first term (A1) is 6.4, and the common difference (d) is 0.8. You're looking to find the value of the 9th term (S9) in this arithmetic progression.

The formula to find the nth term of an arithmetic progression is: $A_n = A_1 + (n - 1) \cdot d$

Where:

• $A_n$ is the nth term
• $A_1$ is the first term
• $n$ is the term number
• $d$ is the common difference

In this case, $A_1 = 6.4$, $d = 0.8$, and $n = 9$: $A_9 = 6.4 + (9 - 1) \cdot 0.8$ $A_9 = 6.4 + 8 \cdot 0.8$ $A_9 = 6.4 + 6.4$ $A_9 = 12.8$

So, the 9th term (S9) in this arithmetic progression is 12.8.