Question

S10 Якщо a1=-2 ; a10=-50​

Answer 1

$\displaystyle\bf\\a_{1} =-2\\\\a_{10} =-50\\\\\\S_{10} =\frac{a_{1}+a_{10} }{2} \cdot 10=\bigg(a_{1} +a_{10} \bigg)\cdot 5=\bigg(-2-50\bigg)\cdot 5=-25\cdot 5=-125\\\\\\Otvet: \ S_{10}=-125$