Question

помогите пожалуйстааа срочно надо

Answer 1

Ответ:

S10=295

Решение

Фотографии решения прикрепила ниже

88=а1+11*9

88=а1+99

а1=-99+88

а1=-11

Answer 2

$\displaystyle\bf a _{4} = 16 \\ a _{12} = 88 \\ a_{n} = a_{1} + (n - 1)d\\ \\ \left \{ {{a_{4} = a_{1} + 3d} \atop {a_{12} = a_{1} + 11d}} \right. \\ \\ \left \{ {{ a_{1} + 3d = 16 \: \: | \times ( - 1) } \atop { a_{1} + 11d = 88}} \right. \\ \\ + \left \{ {{ - a_{1} - 3d = - 16 } \atop { a_{1} + 11d = 88}} \right. \\ \\ 11d - 3d = 88 - 16 \\ 8d = 72 \\ d = 72 \div 8 \\ d = 9 \\ \\ a_{1} + 3 \times 9 = 16 \\ a_{1} + 27 = 16 \\ a_{1} = 16 - 27 \\ a_{1} = - 11 \\ \\ a_{10} = a_{1} + 9d = - 11 + 9 \times 9 = - 11 + 81 = 70 \\ S_{n} = \frac{a_{1} + a_{n}}{2} \times n \\ S_{10} = \frac{a_{1} + a_{10}}{2} \times 10 = 5(a_{1} + a_{10}) = \\ = 5 \times ( - 11 + 70) = 5 \times 59 = 295$