4хх-2х(2х+5)=4х^2*2х+4х^2*5 -2х*2х -2х*5=8х^3+20х^2-4х^2-10х=8х^3+16х^2-10х=4х^3+8х-5
B(1)=2
b(2)= b(1)×q=2×3=6
b(3)=b(2)×q= 6×3= 18
S(3)= 2+6+18= 26
a3=4
a9=22
a3=a1+2d
a9= a1+8d
a1=4-2d
a1=22-8d
4-2d=22-8d
6d=18
d=3
a1= 4-6= -2
a2021= a1+2020d= -2+2020*3= 6058