Question

a5=18 a8=33 надо найти а1-? d-?

Answer 1

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