Question

Алгебра. Даю 20 баллов. Задание 2. С объяснением.

Answer 1

$\displaystyle\bf\\a_{21} =-10\\\\a_{22} =-5,5\\\\a_{22} =a_{21} +d\\\\d=a_{22} -a_{21} =-5,5-(-10)=-5,5+10=4,5\\\\a_{21} =a_{1} +20d\\\\a_{1} =a_{21} -20d=-10-20\cdot4,5=-10-90=-100\\\\\boxed{a_{1} =-100}$