Minimum area of a Polygon with three points given

Given three points of a regular polygon( n > 3), find the minimum area of a regular polygon (all sides same) possible with the points given .

Examples:

Input : 0.00 0.00
1.00 1.00
0.00 1.00
Output : 1.00
By taking point (1.00, 0.00) square is
formed of side 1.0 so area = 1.00 .

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

One thing to note in question before we proceed is that the number of sides must be at least 4 (note n > 3 condition)..

Here, we have to find the minimum area possible for a regular polygon, so to calculate minimum possible area, we need calculate required value of n . As the side length is not given, so we first calculate circumradius of the triangle formed by the points. It is given by the formula
R = abc / 4A
where a, b, c are the sides of the triangle formed and A is the area of the traingle. Here, the area of triangle can be calculated by Heron’s Formula .

After calculating circumradius of the triangle, we calculate the area of the polygon by the formula

A = nX ( sin(360/n) xr2 /2 )

Here r represents the circumradius of n-gon ( regular polygon of n sides ) .
But, first we have to calculate value of n . To calculate n we first have to calculate all the angles of triangle by the cosine formula
cosA = ( b2+c2-a2 ) / 2bc
cosB = ( a2+c2-b2 ) / 2ac
cosC = ( a2+b2-c2 ) / 2ab

Then, n is given by
n = pi / GCD (A , B, C )
where A, B and C are the angles of the triangle . After calculating n we substitute this value to the formula for calculating area of polygon .

Below is the implementation of the given approach :

C++

 // CPP program to find minimum area of polygon of // number of sides more than three with given three points. #include using namespace std;    // assigning pi value to variable const double pi = 3.14159265359;    // calculating gcd value of two double values . double gcd(double x, double y) {     return fabs(y) < 1e-4 ? x : gcd(y, fmod(x, y)); }    // Calculating minimum area of polygon through this function . double min_area_of_polygon(double Ax, double Ay, double Bx,                              double By, double Cx, double Cy) {     double a, b, c, Radius, Angle_A, Angle_B, Angle_C,                                semiperimeter, n, area;        // calculating the length of the sides of the triangle      // formed from given points a, b, c represents the      // length of different sides of triangle .     a = sqrt((Bx - Cx) * (Bx - Cx) + (By - Cy) * (By - Cy));     b = sqrt((Ax - Cx) * (Ax - Cx) + (Ay - Cy) * (Ay - Cy));     c = sqrt((Ax - Bx) * (Ax - Bx) + (Ay - By) * (Ay - By));        // here we have calculated the semiperimeter of a triangle .     semiperimeter = (a + b + c) / 2;        // Now from the semiperimeter area of triangle is derived     // through the heron's formula .     double area_triangle = sqrt(semiperimeter * (semiperimeter - a)                                 * (semiperimeter - b)                                 * (semiperimeter - c));        // thus circumradius of the triangle is derived from the      // sides and area of the triangle calculated .     Radius = (a * b * c) / (4 * area_triangle);        // Now each angle of the triangle is derived from the sides     // of the triangle .     Angle_A = acos((b * b + c * c - a * a) / (2 * b * c));     Angle_B = acos((a * a + c * c - b * b) / (2 * a * c));     Angle_C = acos((b * b + a * a - c * c) / (2 * b * a));        // Now n is calculated such that area is minimum for     // the regular n-gon .     n = pi / gcd(gcd(Angle_A, Angle_B), Angle_C);        // calculating area of regular n-gon through the circumradius     // of the triangle .     area = (n * Radius * Radius * sin((2 * pi) / n)) / 2;        return area; }    int main() {     // three points are given as input .     double Ax, Ay, Bx, By, Cx, Cy;     Ax = 0.00;     Ay = 0.00;     Bx = 1.00;     By = 1.00;     Cx = 0.00;     Cy = 1.00;        printf("%.2f", min_area_of_polygon(Ax, Ay, Bx, By, Cx, Cy));     return 0; }

Python3

 # Python3 program to find minimum area of  # polygon of number of sides more than three # with given three points.     # from math lib import every function from math import *    # assigning pi value to variable  pi = 3.14159265359    # calculating gcd value of two double values .  def gcd(x, y) :        if abs(y) < 1e-4 :         return x     else :         return gcd(y, fmod(x, y))       # Calculating minimum area of polygon  # through this function .  def min_area_of_polygon(Ax, Ay, Bx,                          By, Cx, Cy) :        # calculating the length of the sides of      # the triangle formed from given points      # a, b, c represents the length of different     # sides of triangle     a = sqrt((Bx - Cx) * (Bx - Cx) +              (By - Cy) * (By - Cy))     b = sqrt((Ax - Cx) * (Ax - Cx) +               (Ay - Cy) * (Ay - Cy))     c = sqrt((Ax - Bx) * (Ax - Bx) +              (Ay - By) * (Ay - By))         # here we have calculated the semiperimeter      # of a triangle .      semiperimeter = (a + b + c) / 2        # Now from the semiperimeter area of triangle      # is derived through the heron's formula      area_triangle = sqrt(semiperimeter *                          (semiperimeter - a) *                          (semiperimeter - b) *                          (semiperimeter - c))        # thus circumradius of the triangle is derived      # from the sides and area of the triangle calculated     Radius = (a * b * c) / (4 * area_triangle)        # Now each angle of the triangle is derived      # from the sides of the triangle     Angle_A = acos((b * b + c * c - a * a) / (2 * b * c))     Angle_B = acos((a * a + c * c - b * b) / (2 * a * c))     Angle_C = acos((b * b + a * a - c * c) / (2 * b * a))        # Now n is calculated such that area is      # minimum for the regular n-gon      n = pi / gcd(gcd(Angle_A, Angle_B), Angle_C)        # calculating area of regular n-gon through      # the circumradius of the triangle     area = (n * Radius * Radius *              sin((2 * pi) / n)) / 2        return area    # Driver Code if __name__ == "__main__" :        # three points are given as input .      Ax = 0.00     Ay = 0.00     Bx = 1.00     By = 1.00     Cx = 0.00     Cy = 1.00        print(round(min_area_of_polygon(Ax, Ay, Bx,                                      By, Cx, Cy), 1))    # This code is contributed by Ryuga

Output:

1.00

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