Question

a1=5 a9=37 S12=?? помогте пжалуста

Answer 1

a1+8d=37
8d=37–5
8d=32
d=4
2a1+11d
S12 = ------------ • 12 = (2a1+11d)•6 =
2

= (2•5+11•4)•6 = 324