как известно, an=a1*q^(n-1)
X²(x-1)+x(x-1)²=x(x-1)*(x+x-1)=x(x-1)(2x-1)
1. a1=7 a6=25
a6=7+d*5 7+5d=25 5d=18 d=18/5=3.6
a4=7+3d=4+3*3.6=14.8
2. a10=1.9 a16=6.1 a1,d?
a1+9d=1.9
a1+15d=6.1
15d-9d=6.1-1.9
6d=5.1 d=0.85 a1=1.9-9*0.85=1.9-7.65=-5.75
X–3y=4
2x+y=15
2x–6y=8
2x+y=15
2x–6y-(2x+y)=8-15
2x-6y-2x-y= -7
-7y= -7
y=1
x-3y=4
x=4+3y
x=4+3×1=7