Question

СРОЧНО!
в арифметичній прогресії S3=27. Знайдіть a2?

Answer 1

$\displaystyle\bf\\S_{3} =27\\\\a_{1} +a_{2} +a_{3} =27\\\\a_{1} +a_{1} +d+a_{1} +2d=27\\\\3a_{1}+3d=27\\\\3\cdot(a_{1}+d)=27\\\\a_{1} +d=9\\\\\\a_{2} =a_{1} +d=9\\\\Otvet: \ a_{2} =9$