x(x^2-2x+2x-4)-x^3+8x=16
x^3-2x^2+2x^2-4x-x^3+8x=16
-4x+8x=16
4x=16
x=4
Возможно, подразумевалось:
<span>X(X+2)(X-2)-X(X²-8)=16</span>
<span></span>
<span>х(х²-4)-х(х²-8)=16</span>
<span>х³-4х-х³+8х=16</span>
<span>4х=16</span>
<span>х=4</span>
x*(x-1)*(x-1)-(x-2)*(x²+2x+4)=x*(x-1)²-(x³-2³)=x*(x²-2x+1)-x³+8=
=x³-2x²+x-x³+8=-2x²+x+8.
S=(b1*(q^n-1))/(q-1)
1820=(b1*(729-1))/(3-1),
b1=5
b5=b1*q^4=5*81=405
b1+b5=410