Question

A6-? d-? если a5+a7=54 a2=39

Answer 1

$a_{6} =\frac{a_{5}+a_{7}}{2}=\frac{54}{2}=27\\\\\left \{ {{a_{6}=27 } \atop {a_{2}=39 }} \right.\\\\-\left \{ {{a_{1}+5d=27 } \atop {a_{1}+d=39 }} \right.\\\\-------\\\\4d=-12\\\\d=-3$