解二次方程c#2008-08-27 21:01:00

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Quadratic equation

Determine real and complex roots of a quadratic equation ax^2 + bx + c = 0 and check results

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Language: C++
Last Modified: December 15, 2006
Instructions: enter a, b and c roots are evaluated and printed together with a test which uses the roots to evaluate ax^2 + bx + c which should be 0
Snippet //  Determine real and complex roots of a quadratic equation and check results //   ax^2 + bx + c = 0   #include <iostream> #include <math.h> #include <complex> using namespace std;   int main(void) {     float a, b, c, x1, x2, root;     complex<float> z;         cout << "Roots of quadratic equation, Enter a, b and c ? ";     cin >> a >> b >> c;         root = b * b - 4.0f * a * c;                                    // b*b - 4ac     if (root >= 0.0f)                                                    // if +         {         root = sqrt(root);                                         // real roots         x1 = (-b + root) / (2.0f * a);         x2 = (-b - root) / (2.0f * a);         cout << "Real roots " << x1 << " and " << x2 << endl;         cout << "Test " << a * x1 * x1 + b * x1 + c              // check result              << " and " << a * x2 * x2 + b * x2 + c << endl;         }     else         {                                                       // complex roots         root = sqrt(-root) / (2.0f * a);         x1 = -b / (2.0f * a);         cout << "Complex roots " << x1 << " +- i " << root << endl;         z = complex<float>(x1, root);         cout << "Test " << a * z * z + b * z + c;                // check result         z = complex<float>(x1, -root);         cout << " and " << a * z * z + b * z + c << endl;            }     system("pause");     return 0; }   Copy & Paste // Determine real and complex roots of a quadratic equation and check results // ax^2 + bx + c = 0 #include <iostream> #include <math.h> #include <complex> using namespace std; int main(void) { float a, b, c, x1, x2, root; complex<float> z; cout << "Roots of quadratic equation, Enter a, b and c ? "; cin >> a >> b >> c; root = b * b - 4.0f * a * c; // b*b - 4ac if (root >= 0.0f) // if + { root = sqrt(root); // real roots x1 = (-b + root) / (2.0f * a); x2 = (-b - root) / (2.0f * a); cout << "Real roots " << x1 << " and " << x2 << endl; cout << "Test " << a * x1 * x1 + b * x1 + c // check result << " and " << a * x2 * x2 + b * x2 + c << endl; } else { // complex roots root = sqrt(-root) / (2.0f * a); x1 = -b / (2.0f * a); cout << "Complex roots " << x1 << " +- i " << root << endl; z = complex<float>(x1, root); cout << "Test " << a * z * z + b * z + c; // check result z = complex<float>(x1, -root); cout << " and " << a * z * z + b * z + c << endl; } system("pause"); return 0; }
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