Объяснение:
-2,8*1 3/7=-2 4/5*1 3/7=-14/5*10/7=-4
=-4а^3b^5c^7d
коэффициент равен (-4)
Розв'язання завдання додаю
1)
a1=-16
d=a2-a1=-10-(-16)=-10+16=6
s17=(a1+a17)*17/2=(a1+a1+16*d)*17/2=(2a1+16d)*17/2=2(a1+8d)*17/2=(a1+8d)*17=(-16+8*6)*17=(-16*48)*17=32*17=544
an=2+5n
Свойство арифметической прогрессии:
![\frac{a_{n-1}+a_{n+1}}{2}=a_{n}](https://tex.z-dn.net/?f=%5Cfrac%7Ba_%7Bn-1%7D%2Ba_%7Bn%2B1%7D%7D%7B2%7D%3Da_%7Bn%7D)
Подставим и упростим:
![\frac{(2+5(n-1))+(2+5(n+1))}{2}=2+5n](https://tex.z-dn.net/?f=%5Cfrac%7B%282%2B5%28n-1%29%29%2B%282%2B5%28n%2B1%29%29%7D%7B2%7D%3D2%2B5n)
![\frac{2+5n-5+2+5n+5}{2}=2+5n](https://tex.z-dn.net/?f=%5Cfrac%7B2%2B5n-5%2B2%2B5n%2B5%7D%7B2%7D%3D2%2B5n)
![\frac{4+10n}{2}=2+5n](https://tex.z-dn.net/?f=%5Cfrac%7B4%2B10n%7D%7B2%7D%3D2%2B5n)
![\frac{2(2+5n)}{2}=2+5n](https://tex.z-dn.net/?f=%5Cfrac%7B2%282%2B5n%29%7D%7B2%7D%3D2%2B5n)
ЧТД