calculatorDegree method

double calculatorDegree(
  1. double x1,
  2. double y1,
  3. double x2,
  4. double y2,
  5. double x3,
  6. double y3,
)

三个点：圆心A，半径r，度数0的点B,任意点C. 先计算∠BAC的度数（弧度）。

Implementation

double calculatorDegree(
    double x1, double y1, double x2, double y2, double x3, double y3) {
  double radian = 0;

  double ab = getDistance(x1, y1, x2, y2);
  double ac = getDistance(x1, y1, x3, y3);
  double bc = getDistance(x2, y2, x3, y3);

  double value = (ab * ab + ac * ac - (bc * bc)) / (2 * ab * ac);

  radian = acos(value);

  return radian;
}