圓心 圓上點運算

float x = 5.0f;
float y = 0.0f;
double z = Math.pow(x, 2) + Math.pow(y, 2);
// 求斜邊
double z2 = Math.sqrt(z);
double z1 = (double) (x / z2);
// 反餘弦求角度
System.out.println(Math.toDegrees(Math.acos(z1)));

// 圓上任意一點的座標

int r = 10;
double angle = Math.toDegrees(Math.acos(z1));
double x1 = 0 + r * Math.cos(angle * Math.PI / 180);
double y1 = 0 + r * Math.cos(angle * Math.PI / 180);