Quadratic Equation from Sum and Product

Rarely Tested

Quadratic Equation from Sum and Product

## Formula

If:

$$\alpha+\beta=S$$

and:

$$\alpha\beta=P$$

then the quadratic equation having roots $$\alpha,\beta$$ is:

$$x^2-Sx+P=0$$

## Usage

- Used to construct a quadratic when only the sum and product of roots are known.

Question 1

If the function $$f(x) = 2x^3 - 9ax^2 + 12a^2x + 1$$, $$a > 0$$ has a local maximum at $$x = \alpha$$ and a local minimum at $$x = \alpha^2$$, then $$\alpha$$ and $$\alpha^2$$ are the roots of the equation :

Question 2

Let $$\alpha, \beta$$ be the roots of the equation $$x^2 + 2\sqrt{2}x - 1 = 0$$. The quadratic equation, whose roots are $$\alpha^4 + \beta^4$$ and $$\frac{1}{10}(\alpha^6 + \beta^6)$$, is :

Question 3

Let $$p$$ and $$q$$ be two numbers such that $$p + q = 2$$ and $$p^4 + q^4 = 272$$. Then $$p$$ and $$q$$ are roots of the equation:

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