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- N8b – Surds
- A4f – Simplifying, multiplying and dividing algebraic fractions
- A5a – Rearranging formulas to change the subject
- A17a – Solving simple linear equations in one unknown algebraically
- A17b – Solving linear equations in one unknown algebraically where the unknown is on both sides of the equation
- A18a – Solving quadratic equations by factorising

# The quadratic formula

\({\color{Black}{\large \text{If }ax^{2} + bx +c = 0}}\)

_\({\color{Black}{\large \text{then }x = \dfrac{-b \pm \sqrt{b^{2}-4ac}}{2a}}}\)

_\({\large \color{#e0e0e0}{\text{then x }}\color{Black}{= \dfrac{-b}{2a} \pm \dfrac{\sqrt{b^{2}-4ac}}{2a}}}\)

_\({\color{Black}{\large \text{The line }x = -\dfrac{b}{2a}\text{ is the line }}}\)\({\color{Black}{\large \text{of symmetry for the curve }}}\) \({\color{Black}{\large y=ax^{2} + bx +c}}\)

_\({\color{Black}{\large \text{Also, }\dfrac{\sqrt{b^{2}-4ac}}{a} \text{ is the }}}\) \({\color{Black}{\large \text{distance between the }}}\) \({\color{Black}{\large \text{solutions of }ax^{2} + bx +c = 0 }}\). \({\color{Black}{\large \text{Can you see why?}}}\)

# Solving quadratic equations using the quadratic formula

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