#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
 
using namespace std;
 
#define PI 3.14159265
 
double integrate(double x1, double x2, double r)
{
    double r1 = (std::sqrt(r*r - x1*x1)/2 * x1 + (9*asin(x1/3))/2);
    double r2 = (std::sqrt(r*r - x2*x2)/2 * x2 + (9*asin(x2/3))/2);
 
    return 4 * (r2 - r1);
}
 
void calculate(double radius)
{
    double Result = integrate(0, radius, radius);//((9.0/4.0) + (sqrt(6) / 2.747319)) * radius * radius;
    double realResult = PI * radius * radius;
 
    printf("The area of the circle with radius %lf is %lf.\n",radius,Result);
    printf("The real area of the circle is %lf.",realResult);
    cout << endl;
}
 
int main(int nNumberofArgs,char* pszArgs[])
{
    double radius;
    cout << "Enter radius: ";
    cin >> radius;
 
    calculate(radius);
 
    //system("PAUSE");
    return 0;
}

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