WAEC Mathematics: Finding the Maximum Value of a Quadratic Function

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For the model S = 200 + 50x − 2x², the coefficient of x² is negative. This means the graph opens downward, so the savings reach a maximum value. Write the expression as S = −2x² + 50x + 200. Using x = −b/(2a): x = −50 / [2(−2)] = 12.5. Therefore, the monthly savings stop increasing after 12.5 months. Substitute x = 12.5 into the equation: S = 200 + 50(12.5) − 2(12.5)² = 512.5. The maximum monthly saving is $512.50.

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