Algebra-1

Question Analysis
This question tests the student's ability to find the range of a quadratic function given in standard form. The function opens downward, so the vertex represents the maximum point.

Key Concept Explanation
The range of a quadratic function depends on the vertex's y-coordinate (k) and the sign of the coefficient a. For a parabola that opens downward ( ), the range is all y-values less than or equal to the vertex's y-coordinate.

Step-by-step Solution
1. Convert the function to vertex form by completing the square: .
2. Simplify to get the vertex form:

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