а31=а1+(n-1)d
147=х+30*6
147-180=х
х=-33
bn = b₁ * qⁿ⁻¹
=19/81
q=±0.79
1.a(n) =a1+d*(n-1)
a31=a1+6*30
a1=a(n)-d*(n-1)
a1=147-6*30
a1=147-180
a1=(-33)
2.b(n)=b1*q^(n-1)
q^(n-1)=b(n)/b1
q^6=19/81
=19/81![q = \sqrt[6]{ \frac{19}{81} }](/tpl/images/3184/8894/2f709.png)
