Question

............. ............. ​

Answer 1

Ответ:

$a_{3} = 15.8\\a_{4} = 23.2\\S_{4} = 48.4$

Объяснение:

$a_{2}- a_{1}=d\\d=8.4-1=7.4\\a_{3} =a_{2}+d=8.4+7.4=15.8\\a_{4} =a_{3}+d=15.+7.4=23.2\\\\S=\frac{a_{1}+a_{n} }{2} *n\\S=\frac{1+23.2}{2} * 4= 48.4$