Algebra-1

Question Analysis
This question tests the understanding of the vertex form of a quadratic function and the properties of the vertex, specifically using the given maximum value and a point on the parabola to find the x-coordinate of the vertex.

Key Concept Explanation
The vertex form of a quadratic function is , where is the vertex. The vertex is the point where the parabola reaches its maximum or minimum value. For a parabola that opens downwards, the vertex is the highest point.

Step-by-step Solution
1. Identify the given information: The parabola opens downwards, . The maximum value is 9, so . The parabola passes through the point .
2. Use the vertex form: Substitute the point into the vertex form . This gives

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