Question

a5=18 a8=33 надо найти а1-? d-?

Answer 1

$\left \{ {{a_{8}=33 } \atop {a_{5}=18 }} \right.\\\\-\left \{ {{a_{1}+7d=33 } \atop {a_{1}+4d=18 }} \right. \\-------\\3d=15\\d=5\\a_{1}=18-4d=18-4*5=18-20=-2\\a_{1}=-2$