Question

Номер , только б),г)

(ещё в профиле номер 393 б).))

Answer 1

$a_{n} = a_{1} + (n - 1)d$

$S_{n} = \frac{2a_{1} + d(n - 1)}{2} \times n$

б)

$9.5 = 0.5 + (4 - 1)d \\ \\ 9.5 - 0.5 = 3d \\ \\ d = \frac{9}{3} \\ \\ d = 3$

$S_{10} = \frac{2 \times 0.5 + 3(10 - 1)}{2} \times 10 = \frac{1 + 3 \times 9}{2} \times 10 = \frac{28}{2} \times 10 = 14 \times 10 = 140$

г)

$a_{4} = 10 \: \: \: \: \: \: a_{7} = 19 \\ a_{7} - a_{4} = 3d$

$19 - 10 = 9 \\ 9 = 3d \\ d = 3$

$10 = a_{1} + (4 - 1) \times 3 \\ 10 =a_{1} + 9 \\ a_{1} = 1$

$S_{10} = \frac{2 \times 1 + 3(10 - 1)}{2} \times 10 = 2 + 27 \times 5 = 29 \times 5 = 145$

Answer 2

ответ во вложении

Объяснение: