Cardano's Formula Calculator

Cardano's Formula Mathematical Formula
Step-by-step Instructions

Cardano's Formula is used to find one real root of a cubic equation in the form: \[ ax^3 + bx^2 + cx + d = 0 \].

Formula:

\[ x = \sqrt[3]{\frac{-q}{2} + \sqrt{\frac{q^2}{4} + \frac{p^3}{27}}} + \sqrt[3]{\frac{-q}{2} - \sqrt{\frac{q^2}{4} + \frac{p^3}{27}}} - \frac{b}{3a} \]

Explanation:

  • p: Intermediate variable calculated as \( b - \frac{3a^2}{9} \)
  • q: Intermediate variable calculated as \( \frac{2a^3}{27} - \frac{ab}{3} + c \)
  • Cube Roots:
    • \( \sqrt[3]{\frac{-q}{2} + \sqrt{\frac{q^2}{4} + \frac{p^3}{27}}} \)
    • \( \sqrt[3]{\frac{-q}{2} - \sqrt{\frac{q^2}{4} + \frac{p^3}{27}}} \)
  • Calculation: The cube roots are added together and then subtracted by \( \frac{b}{3a} \) to find the real root \( x \).

Cardano's Formula Mathematical Formula
Step-by-step Instructions

Cardano's Formula Calculator

Cardano's Formula Mathematical Formula
Step-by-step Instructions

Step-by-Step Solution:

  1. Input the coefficients \( a \), \( b \), \( c \), and \( d \).
  2. Calculate \( p \) and \( q \):
    • \( p = \frac{-b^2}{3a^2} + \frac{c}{a} \)
    • \( q = \frac{2b^3}{27a^3} - \frac{bc}{3a^2} + \frac{d}{a} \)
  3. Calculate the discriminant \( \Delta = \frac{q}{2}^2 + \frac{p}{3}^3 \).
  4. Check \( \Delta \) value and determine the number of real solutions:
    • If \( \Delta > 0 \), there is one real solution and two complex solutions.
    • If \( \Delta = 0 \), there are two real solutions and one repeated real solution.
    • If \( \Delta < 0 \), there are three distinct real solutions.
  5. Solve for solutions depending on the case:
    • For \( \Delta > 0 \):
      • Calculate \( u = \sqrt[3]{-\frac{q}{2} + \sqrt{\Delta}} \) and \( v = \sqrt[3]{-\frac{q}{2} - \sqrt{\Delta}} \).
      • One real solution: \( x_1 = u + v - \frac{b}{3a} \)
      • Complex solutions: \( x_2 \) and \( x_3 \) (as complex numbers).
    • For \( \Delta = 0 \):
      • Calculate \( u = \sqrt[3]{-\frac{q}{2}} \).
      • Two real solutions: \( x_1 = 2u - \frac{b}{3a} \) and \( x_2 = -u - \frac{b}{3a} \)
    • For \( \Delta < 0 \):
      • Calculate \( r = \sqrt{\frac{q^2}{4} - \Delta} \) and \( \theta = \arctan\left(\frac{\sqrt{-\Delta}}{-\frac{q}{2}}\right) \).
      • Three real solutions: \( x_1 \), \( x_2 \), and \( x_3 \) (using trigonometric functions).
  6. Finalize the solutions \( x_1 \), \( x_2 \), and \( x_3 \) depending on the case and the values of \( a \), \( b \), \( c \), and \( d \).

Final Solutions:

Based on the calculation and analysis, the solutions for the given quadratic equation are:

  • Solution \( x_1 \):
  • Solution \( x_2 \):
  • Solution \( x_3 \):

Cardano's Formula Mathematical Formula

Examples for Each Case of \( \Delta \) in Cardano's Formula

Case: \( \Delta > 0 \)

Example Coefficients: \( a = 1 \), \( b = -6 \), \( c = 11 \), \( d = -6 \)

Calculation Steps:

  • \( p = \frac{-(-6)^2}{3(1)^2} + \frac{11}{1} = -2 \)
  • \( q = \frac{2(-6)^3}{27(1)^3} - \frac{(-6) \cdot 11}{3(1)^2} + \frac{-6}{1} = 7 \)
  • \( \Delta = \frac{7}{2}^2 + (-2/3)^3 = \frac{529}{108} > 0 \)

Final Solutions:

  • \( u \approx 1.365 \)
  • \( v \approx -3.365 \)
  • One real solution: \( x_1 = 4 \)
  • Complex solutions: \( x_2 \approx -1.182 + 3.529i \) and \( x_3 \approx -1.182 - 3.529i \)

Case: \( \Delta = 0 \)

Example Coefficients: \( a = 1 \), \( b = -3 \), \( c = 3 \), \( d = -1 \)

Calculation Steps:

  • \( p = \frac{-(-3)^2}{3(1)^2} + \frac{3}{1} = 1 \)
  • \( q = \frac{2(-3)^3}{27(1)^3} - \frac{(-3) \cdot 3}{3(1)^2} + \frac{-1}{1} = -1 \)
  • \( \Delta = \frac{1}{4} + \frac{1}{27} = 0 \)

Final Solutions:

  • \( u = \sqrt[3]{\frac{1}{2}} \)
  • Two real solutions: \( x_1 = 1 \) and \( x_2 = -1 \)

Case: \( \Delta < 0 \)

Example Coefficients: \( a = 1 \), \( b = 1 \), \( c = 1 \), \( d = 1 \)

Calculation Steps:

  • \( p = \frac{-(1)^2}{3(1)^2} + \frac{1}{1} = -\frac{2}{3} \)
  • \( q = \frac{2(1)^3}{27(1)^3} - \frac{(1) \cdot 1}{3(1)^2} + \frac{1}{1} = -\frac{2}{27} \)
  • \( \Delta = -\frac{217}{729} < 0 \)

Final Solutions:

  • Three real solutions (using trigonometric functions, too complex for example here)