program p183323;

const
  a = 0;{нижний предел}
  b = 1.5708;{верхний предел}
  n = 10;{разбиение}

function f(x: real): real;
begin
  f := x * sin(x);
end;

function IntegralPriam(a, b: real): real;
{метод прямоугольников}
var
  h, k, s: real;
  i: Integer;
begin
  h := (b - a)/N;
  s := 0;
  k := a + h/2;
  for i := 0 to N - 1 do
    begin
      s := s + f(k);
      k := k + h;
    end;
  s := s*h;

  IntegralRect := s;
end;

function IntegralTrap(a, b: real): real;
{метод трапеций}
var
  h, k, s: real;
  i: Integer;
begin
  h := (b - a)/N;
  s := (f(a) + f(b))/2;
  k := a;
  for i := 1 to N - 1 do
    begin
      k := k + h;
      s := s + f(k);
    end;
  s := s*h;

  IntegralTrap := s;
end;

function IntegralSimpson(a, b: real): real;
{метод симпсона}
var
  h, k, s: real;
  i: Integer;
begin
  h := (b - a)/N;
  s := 0;
  k := a;
  for i := 1 to N - 1 do
    begin
      k := k + h;
      if i mod 2 = 0 then
        s := s + 2*f(k)
      else
        s := s + 4*f(k);
    end;

  s := (s + f(a) + f(b))*h/3;

  IntegralSimpson := s;
end;

begin
  writeln('Metodom Piamougolnikov = ', IntegralPriam(a, b):0:5);
  writeln('Metodom Trapecij = ', IntegralTrap(a, b):0:5);
  writeln('Metodom Simpsona = ', IntegralSimpson(a, b):0:5);
  readln
end.