Предмет: Алгебра, автор: ivan6994

Помогите пожалуйста срочно надо решить.))
Решение и ответы пожалуйста. Даю 16 баллов!! ​

Приложения:

Ответы

Автор ответа: nktselepov
1

1)

a_{12}=16,5+(-1,5)(12-1)=16,5-16,5=0

S_{12} =\frac{(16,5+0)*12}{2} =99

2)

a_1=3*1+2=5

a_2=3*2+2=8

d=8-5=3

a_{40}=3*40+2=122

S_{40}=\frac{(5+122)*40}{2} =2540

3)

\frac{a7-a1}{6}=d \\d=3 \\S10=\frac{2a1+(n-1)d}{2} *n\\S_{10}=\frac{2*8+3*9}{2} *10=215

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