#include <iostream>
#include <iomanip>
#include <cmath>
#include <vector>
#include <utility>
 
#define MINX (-20.0f)
//MAXX Happens to be an upper bound for all zeroes of the function...
#define MAXX (1.0f)
#define NUM_INTERVALS (1000000)
#define NUM_BISECTION_ITERATIONS (30)
 
using namespace std;
 
double f(double x){
	return 5 * x * exp(-x) * cos(x) + 1;
}
 
//Used for Newton's method, if so desired... but that isn't used here.
double df(double x){
	return -5 * exp(-x)*x*sin(x) + 5 * exp(-x) * x * sin(x) - 5 * exp(-x) * x * cos(x);
 
}
 
double bisection_method(double x0, double x1){
	for (unsigned int i = 0; i < NUM_BISECTION_ITERATIONS; i++){
		double midpoint = 0.5*x0 + 0.5*x1;
		f(x0) * f(midpoint) < 0 ? x1 = midpoint : x0 = midpoint;
	}
	return 0.5*x0 + 0.5*x1;
}
 
int main(int argc, char** argv){
	vector<pair<double, double>> relevant_intervals;
	for (unsigned int i = 0; i < NUM_INTERVALS - 1; i++){
		double x0 = MINX + (MAXX - MINX) / NUM_INTERVALS * (i);
		double x1 = MINX + (MAXX - MINX) / NUM_INTERVALS * (i + 1);
		if (f(x0) * f(x1) < 0)
			relevant_intervals.push_back(make_pair(x0, x1));
	}
	cout << fixed << setprecision(20);
	for (const auto & x : relevant_intervals){
		cout << "One solution is approximately " << bisection_method(x.first, x.second) << endl;
	}
}

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