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Solving quadratic equations using the quadratic formula - Higher

The quadratic formula can be used to solve quadratic equations that will not factorise. You will need to learn this formula, as well as understanding how to use it.

Example

Solve \(x^2 + 6x - 12 = 0\) using the quadratic formula.

First, identify the value of \(a\), \(b\) and \(c\). In this example, \(a = 1\), \(b = 6\) and \(c = -12\).

Substitute these values into the quadratic formula:

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

\(x = \frac{(- 6) \pm \sqrt{6^2 - 4 \times 1 \times (-12)}}{2 \times 1}\)

\(x = \frac{(-6) \pm \sqrt{36 + 48}}{2}\)

\( x = \frac{(-6) \pm \sqrt{84}}{2}\)

To calculate the decimal answers, work out each answer in turn on a calculator.

\(x = \frac{(-6) \pm \sqrt{84}}{2}\)

The first solution is \(x = \frac{(-6) + \sqrt{84}}{2} = 1.58\) (2 dp).

The second solution is \(x = \frac{(-6) - \sqrt{84}}{2} = -7.58\) (2 dp).

Question

Solve \(2x^2 - 10x + 3 = 0\) using the quadratic formula.