const fi='kt.txt'

fo='kq.out'

var f1,f2:text;

s:string;

i,dem,d:integer;

begin

assign(f1,fi); reset(f1);

assign(f2,fo); rewrite(f2);

readln(f1,s);

d:=length(s);

dem:=0;

for i:=1 to d do 

 if s[i]='e' then inc(dem);

writeln(f2,dem);

close(f1);

close(f2);

end.

\(S=\dfrac{1}{2^2}+\dfrac{1}{\left(2.2\right)^2}+\dfrac{1}{\left(2.3\right)^2}+...+\dfrac{1}{\left(2.10\right)^2}\)

\(=\dfrac{1}{2^2}+\dfrac{1}{2^2.2^2}+\dfrac{1}{2^2.3^2}+...+\dfrac{1}{2^2.10^2}\)

\(=\dfrac{1}{2^2}\left(1+\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{10^2}\right)\)

\(< \dfrac{1}{2^2}\left(1+\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{9.10}\right)\)

\(=\dfrac{1}{4}\left(1+1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)\)

\(=\dfrac{1}{4}\left(2-\dfrac{1}{10}\right)< \dfrac{1}{4}.2=\dfrac{1}{2}\) (đpcm)

\(Cau.23:\\ N=\left(A_1+T_1+G_1+X_1\right).2=\left(100+200=300+400\right).2=2000\left(Nu\right)\\ L=\dfrac{N}{2}.3,4=\dfrac{2000}{2}.3,4=3400\left(A^o\right)\\ Chon.C\)

\(\left(1\right)4Na+O_2--->2Na_2O\)

\(\left(2\right)Na_2O+H_2O--->2NaOH\)

\(\left(3\right)2NaOH+CO_2--->Na_2CO_3+H_2O\)

\(\left(4\right)Na_2CO_3+H_2SO_4--->Na_2SO_4+H_2O+CO_2\)

\(\left(5\right)Na_2SO_4+BaCl_2--->BaSO_4\downarrow+2NaCl\)

d

D

D

\(\left\{{}\begin{matrix}-5x+3y=22\\3x+2y=22\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}-15x+9y=66\\15x+10y=110\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}-y=-44\\3x+2y=22\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}y=44\\3x=22-2y=22-2\cdot44=22-88=-66\end{matrix}\right.\)

=>\(\left\{{}\begin{matrix}x=-22\\y=44\end{matrix}\right.\)