uses crt;
var a:array[1..255]of integer;
i,n,k,kt:integer;
begin
clrscr;
write('Nhap n='); readln(n);
for i:=1 to n do
begin
write('A[',i,']='); readln(a[i]);
end;
write('Nhap k='); readln(k);
kt:=0;
for i:=1 to n do
if a[i]=k then kt:=1;
if kt=0 then writeln(k,' khong co trong day')
else writeln(k,' co trong day');
readln;
end.
\(\dfrac{s}{13}=\dfrac{2s}{3-vn}+\dfrac{2s}{3+vn}\)
\(\dfrac{s}{13}=\dfrac{2s\left(3+vn\right)+2s\left(3-vn\right)}{9-vn^2}\)
\(\dfrac{s}{13}=\dfrac{12s}{9-vn^2}\)
\(s\left(9-vn^2\right)=12s\cdot13\)
\(s\left(9-vn^2\right)=156s\)
\(9-vn^2=156\)
\(vn^2=-147\)