Question

Найти S12 членов А.П., если а1=6, а11=46

Answer 1

A₁₁ = a₁ + 10d
10d = a₁₁ - a₁ = 46 - 6 = 40
d = 40 : 10 = 4
a₁₂ = a₁ + 11d = 6 + 11 * 4 = 6 + 44 = 50
$S _{12} = \frac{a _{1}+a _{12} }{2} *12= \frac{6+50}{2}*12=56*6=336$