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#include <bits/stdc++.h>
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using namespace std;
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int main() {
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//cin读入优化
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std::ios::sync_with_stdio(false);
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float x1, y1, x2, y2, x3, y3;
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cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
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//求三条边的长度，然后再用海伦公式进行求解
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double a, b, c;
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a = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
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b = sqrt((x1 - x3) * (x1 - x3) + (y1 - y3) * (y1 - y3));
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c = sqrt((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2));
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double p = (a + b + c) / 2;
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//假设在平面内,有一个三角形,边长分别为a、b、c
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//三角形的面积S可由以下公式求得：
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//S=√[p(p-a)(p-b)(p-c)]
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//而公式里的p为半周长：p=(a+b+c)/2
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cout << fixed << setprecision(2) << sqrt(p * (p - a) * (p - b) * (p - c)) << endl;
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return 0;
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}
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