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RE: Cubic Formula Proof Step 2: Applying Vieta's Substitution to Obtain a Quadratic Equation

in MES Science6 days ago

Part 4/5:

After resolving and collecting like terms, the equation can be reduced to a standard quadratic form, enabling the application of the quadratic formula.

Deriving the Quadratic Formula

To solve the quadratic equation, we recall the standard form:

[

x^2 + Px + Q = 0

]

Using the quadratic formula yields:

[

x = \frac{-P \pm \sqrt{P^2 - 4Q}}{2}

]

In our case, the variables convert so that ( z^3 = -\frac{p}{2} ), ( P = \frac{p^2}{4} ), and ( Q = \frac{p^3}{27} ). By substituting these values back, we can clearly express ( z^3 ) in terms of ( p ) and ( Q ), leading us to the final roots of the original cubic equation.

Conclusion