Question

Помогите срочно
a1=4 a7=-8 d-?

Answer 1

$\displaystyle\bf\\a_{1} =4\\\\a_{7} =-8\\\\a_{7} =a_{1}+6d\\\\6d=a_{7} -a_{1} =-8-4=-12\\\\d=-12:6=-2\\\\Otvet; \ d=-2$