B1(q^2+q+1)=26
b1q^3(q^2+q+1)=702
Делим
702/26=27
q^3=27
q=3
b1=26/q^2+q+1
b1=2
S5=b1(q^n-1)/q-1
S5=242
Y'=6x^5-3х²+4х
вот собственно и всё
( 2х - 3)*( 2x + 3 ) - ( 4x + 5)*( x - 3 ) = - 1
4x² - 9 - ( 4x² - 12x + 5x - 15 ) = - 1
4x² - 9 - ( 4x² - 7x - 15 ) = - 1
4x² - 9 - 4x² + 7x + 15 = - 1
7x = - 1 - 6
7x = - 7
x = - 1