В арифметической прогрессии a7 = 8 и a11 = 12,8Найдите a1 и d.. Created by winschool. algebra-ru

В арифметической прогрессии a7 = 8 и a11 = 12,8Найдите a1 и d...

July 2022 2 27 Report

В арифметической прогрессии a7 = 8 и a11 = 12,8
Найдите a1 и d.

dtnth

Verified answer

$a_7=8;a_{11}=12.8$
$a_n=a_1+(n-1)*d$
$a_{11}-a_7=(a_1+(11-1)*d)-(a_1+(7-1)*d)=4d$
$4d=12.8-8=4.8$
$d=4.8:4=1.2$
$a_1=a_n-(n-1)*d$
$a_1=8-(7-1)*1.2=8-6*1.2=8-7.2=0.8$

1 votes Thanks 2

306da $a _{7} =a _{1} +d(n-1)$
$a _{1} +6d=8$
$a _{11} =a _{1} +d(n-1)$
$a _{1} +10d=12,8$

$a _{1} +6d=8$
-
$a _{1} +10d=12,8$
______________________
-4d=-4,8
d=1,2; a1=0,8

0 votes Thanks 1

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