Question

a1=96, n=4, Sn=1200, найти d,n

Answer 1

$a_1=96;n=4;S_n=1200$
$S_n=frac{2a_1+(n-1)*d}{2}*n$
$1200=frac{2*96+(4-1)*d}{2}*4$
$192+3d=600$
$64+d=200$
$d=200-64$
$d=136$
$a_n=a_1+(n-1)*d$
$a_4=96+(4-1)*136=504$