(a+b)^(n)=C^(0)_(n)a^(n)b^(0)+C^(1)_(n)a^(n-1)b^(1)+C^(2)_(n)a^(n-2)b^2+...+[red]C^(k)_(n)a^(n-k)b^(k)[/red] +...+C^(n)_(n)b^(n)
T_(k)=[red]C^(k)_(n)a^(n-k)b^(k) [/red]
Найдем k.
a=(1/2)
b=x^8
n=800
T_(k)=C^(k)_(800)(1/2)^(800-k)(x^8)^(k)
(x^(8))^(k) =x^(6384)
8k=6384
k=798
T_(798)=C^(798)_(800)*(1/2)^(2)*x^(6384)
C^(798)_(800)*(1/2)^(2)=800!/(798!*2!)(1/4)=799*800/8=799*100=[b]7900[/b]