IGCSE Maths / Quadratic equations, curves and inequalities
Forming quadratics from a context
Edexcel International GCSE Maths (4MA1), chapter 22: Quadratic equations, curves and inequalities, specification point 2.7c. Part of the full course.
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Form a quadratic by expressing the context in terms of an unknown, then rearrange so one side is zero and solve. Check the roots against the situation, because an algebraic solution may not make sense in context.