С^(y+1)_(x)=x!/((y+1)!*(x-y-1)!);
С^(y)_(x)=x!/((y)!*(x-y)!);
С^(y+2)_(x):С^(y+1)_(x):С^(y)_(x)=3::5:5 ⇒
С^(y+2)_(x):С^(y+1)_(x)=3:5
С^(y+1)_(x):С^(y)_(x)=5:5
Система:
{(x-y-1)/(y+2)=3/5
{(x-y)/(y+1)=1 ⇒ x=2y+1
(2y+1-y-1)/(y+2)=3/5
5y=3y+6
y=3
x=2*3+1=7
О т в е т.[b] x=7; y=3[/b]