cos()

The cos() returns the cosine of an argument given in radians.

std::cos(n)

Use cos() to return the cosine of 3.1416 radians:

#include <iostream>
#include <cmath>

int main() {
  double x = 3.1416;
  double result;

  result = std::cos(x);

  std::cout << "The cosine of " << x << " radians is " << result << "\n";
  // Output: The cosine of 3.1416 radians is -1
}