y=2x*x+1                           x[2;3]
#include<iostream>
#include<math.h>
double integral_pr(double x, double y, int dx);
double integral_sim(double x, double y, int dx);
double integral_tr(double x, double y, int dx);
void main(void)
{
	double spr, str, ssim, x, y, n;
	int dx, c;
	scanf_s("%lf%lf%d", &x, &y, &dx);
	printf("\n x=%lf y=%lfdx=%d", x, y, dx);
	scanf_s("%d", &c);
	switch (c)
	{
	case 1:
	{   spr = integral_pr(x, y, dx);
	break; }
	case 2:
	{   spr = integral_sim(x, y, dx);

	break; }

	case 3:
	{spr = integral_tr(x, y, dx);
	break; }

	default: {printf("Error");
		getchar();
		getchar(); }
	}
	printf("Result:\n s=%lf", spr);
	getchar();
	getchar();
}
double integral_pr(double x, double y, int dx)
{
	double s, x1, b;
	s = 0;
	b = (y - x) / dx;
	for (x1 = x; x1 < y; x1 = b + x1)
		s += x1*x1 * 2 + 1;
	return s*b;
}
double integral_tr(double x, double y, int dx)
{
	double s, x1, b;
	s = 0;
	b = (y - x) / dx;
	for (x1 = x; x1 < y; x1 = b + x1)
		s += (x1*x1 * 2 + 1) + ((x1 + b)*(x1 + b) * 2 + 1);
	return s*b / 2;
}
double integral_sim(double x, double y, int dx)
{
	double s, x1, b;
	s = 0;
	b = (y - x) / dx;
	for (x1 = x; x1 < y; x1 = b + x1)
		s += x1*x1 * 2 + 1 + 4 * ((x1 + b / 2)*(x1 + b / 2) * 2 + 1) + ((x1 + b)*(x1 + b) * 2 + 1);
	return s*b / 6;
}