S3=48.s6=141 найди d и а1

Question

S3=48.s6=141 найди d и а1

Answer 1

S3=(2a1+2d)*3/2=48⇒a1+d=16⇒a1=16-d
S6=(2a1+5d)*6/2=141⇒2a1+5d=47
32-2d+5d=47
3d=15
d=5
a1=16-5
a1=11