Ешение уравнений по : 864 х+14 х-18=(26 х+8 х++19)-25х

1+а-а²-а³=(1+а)-а²(1+а)=(1-а²)(1+а)=(1-а)(1+а)(1+а)

n=20

a(n)=7+3n

a1=7+3=10

a2=7+3*2=13

d=a2-a1=13-10=3

s(n)=(2a1+d(n-1))*n/2

s(20)=(2*10+3*(20-1))*20/2

s(20)=770

(2+5у)(5у--1)

решение:

(2+5у)(5у--1)=

=(2+5у)(5у-2)-4у+1=

=5у-4у+1

864х+14х-18=26х+8х+1+6х-19-25х

864х+14х-26х-8х-6х+25х=1-19+18

863х=0

х=0: 863

х=0