Quadratic formula I
All quadratic equations can be solved with the quadratic formula I, without having to use the elaborate completing the square, for example.
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Remember
The quadratic formula I may only be applied to quadratic equations in the canonical form (the $x^2$ in the equation is only multiplied by 1).
Given is a quadratic equation in the canonical form: $x^2+\color{green}{p}x+\color{blue}{q}=0$.
The quadratic formula I for solving this equation is:
$x_{1,2} = -\frac{\color{green}{p}}{2} \pm\sqrt{(\frac{\color{green}{p}}{2})^2-\color{blue}{q}}$
Example
Quadratic equation in canonical form: $x^2+\color{green}{6}x+\color{blue}{5}=0$
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Insert $p$ and $q$ in the quadratic formula:
$x_{1,2} = -\frac{\color{green}{p}}{2} \pm\sqrt{(\frac{\color{green}{p}}{2})^2-\color{blue}{q}}$
$x_{1,2} = -\frac{\color{green}{6}}{2} \pm\sqrt{(\frac{\color{green}{6}}{2})^2-\color{blue}{5}}$ -
Simplify term
$x_{1,2} = -3 \pm\sqrt{3^2-5}$
$x_{1,2} = -3 \pm\sqrt{4}$
$x_{1,2} = -3 \pm2$ -
Calculate solutions
$x_{1} = -3+2=-1$
$x_{2} = -3-2=-5$