Question

............. ............. ​

Answer 1

Ответ:

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

Объяснение:

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