Another way of solving a quadratic equation on the form of

$ax^{2}+bx+c=0$

Is to used the quadratic formula. It tells us that the solutions of the quadratic equation are

$x=\frac{-b\pm \sqrt{b^{2}-4ac}}{2a}$

$\: \: where\: \: a\neq 0\: \: and\: \: b^{2}-4ac\geq 0$

Example

Solve the equation

$x^{2}{\color{green} {\, -\, 3}}x{\color{blue} {\, -\, 10}}=0$

$x=\frac{-\left ( {\color{green}{ -\, 3}} \right )\pm \sqrt{\left ( {\color{green} {-\, 3}} \right )^{2}-4\cdot \left ( 1\cdot {\color{blue} {-\, 10}} \right )}}{1\cdot 2}$

$x=\frac{3\pm \sqrt{9+40}}{2}$

${\color{red}{ x_{1}}}=\frac{3{\color{red}{ \, +\, }\sqrt{49}}}{2}= \frac{3+7}{2}= \frac{10}{2}= {\color{red} {5}}$

${\color{red} {x_{2}}}= \frac{3{\color{red}{ \, -\, }\sqrt{49}}}{2}= \frac{3-7}{2}= \frac{-4}{2}= {\color{red} {-2}}$

The expression

$b^{2}-4ac$

Within the quadratic formula is called the discriminant. The discriminant can be used to determine how many solutions the quadratic equation has.

$\begin{matrix} if\: \: b^{2}-4ac>0 & &\: \: \: \: \: \: \: \: \: \: 2\: \: solutions \\ if\: \: b^{2}-4ac=0 & & \: \: \: \: \: \: \: \: \: \: \: \: 1\: \: solution\\ if\: \: b^{2}-4ac<0 & & no\: \: real\: \: solution \end{matrix}$

Here you can check that you've got the right solution

## Video lesson

Solve the equation using the quadratic formula

$x^{2} - 3x-10$