abstract class Triangle extends Polygon implements Form { public static final int numberOfSides = 3; static final boolean triangularInegality(double a, double b,double c) { return ( (a > Math.abs(b-c)) && (a < b+c)); } static final double angle(double a, double b, double c) { return Math.acos((b*b + c*c - a*a)/2/b/c); } public int getnumberOfSides() { return numberOfSides; } public double area () { double sides[] = getSides(); double angleA=angle(sides[0],sides[1],sides[2]); return (sides[1]*sides[2]*Math.sin(angleA)/2); } public String toString() { double s[] = getSides(); return "(" + s[0] + "," + s[1] + "," + s[2] + ")"; } }