Question

помогите пожалуйста 370.​

Answer 1

$\displaystyle\bf\\1)\\\\a_{1} =-23\\\\a_{2} =-20\\\\S_{8} =?\\\\\\a_{2} =a_{1} +d\\\\d=a_{2} -a_{1} =-20-(-23)=-20+23=3\\\\a_{8} =a_{1} +7d=-23+7\cdot 3=-23+21=-2\\\\\\S_{8} =\frac{a_{1} + a_{8} }{2} \cdot 8=(a_{1} +a_{8} )\cdot 4=(-23-2)\cdot 4=-25\cdot 4=-100$

$\displaystyle\bf\\2)\\\\a_{1} =14,2\\\\a_{2} =9,6\\\\S_{8} =?\\\\\\a_{2} =a_{1} +d\\\\d=a_{2} -a_{1} =9,6-14,2=-4,6\\\\a_{8} =a_{1} +7d=14,2+7\cdot (-4,6)=14,2-32,2=-18\\\\\\S_{8} =\frac{a_{1} + a_{8} }{2} \cdot 8=(a_{1} +a_{8} )\cdot 4=(14,2-18)\cdot 4=-3,8\cdot 4=-15,2$