二分求未知数

int main()
{
	double x, y, c;
	while (cin>>x>>y>>c) {
		double low = 0.0;
		double high = y;
		double mid;
		while (low <= high) {
			mid = (low + high) / 2;
			double test = c * (sqrt(x * x - mid * mid) + sqrt(y * y - mid * mid)) - sqrt(y * y - mid * mid) * sqrt(x * x - mid * mid);
			if (MY_ABS(test) < 0.000001) break;
			if (test < 0) low = mid;
			else high = mid;
		}
		printf("%.3lf\n", low);
	}
	return 0;
}