Common Roots of Two Quadratics

Rarely Tested

Common Roots of Two Quadratics

## Formula

For:

$$f(x)=a_1x^2+b_1x+c_1$$

and:

$$g(x)=a_2x^2+b_2x+c_2$$

a common root $\alpha$ satisfies:

$$f(\alpha)=g(\alpha)=0$$

A necessary condition for a common root, when the quadratics are not proportional, is obtained from:

$$\alpha=-\frac{a_2c_1-a_1c_2}{a_2b_1-a_1b_2}$$

provided:

$$a_2b_1-a_1b_2\ne0$$

## Usage

- Used to obtain the common root directly when the quadratic terms are eliminated.

Question 1

Let $$\lambda \neq 0$$ be in $$R$$. If $$\alpha$$ and $$\beta$$ are the roots of the equation, $$x^2 - x + 2\lambda = 0$$ and $$\alpha$$ and $$\gamma$$ are the roots of the equation, $$3x^2 - 10x + 27\lambda = 0$$, then $$\frac{\beta\gamma}{\lambda}$$ is equal to:

Question 2

Let $$\lambda \neq 0$$ be a real number. Let $$\alpha, \beta$$ be the roots of the equation $$14x^2 - 31x + 3\lambda = 0$$ and $$\alpha, \gamma$$ be the roots of the equation $$35x^2 - 53x + 4\lambda = 0$$. Then $$\frac{3\alpha}{\beta}$$ and $$\frac{4\alpha}{\gamma}$$ are the roots of the equation:

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