Answer:
C
Step-by-step explanation:
The area of a square is the square of the side length. When the side length x=2.5 cm, the area is the square of that value.
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A(x) = x²
A(2.5 cm) = (2.5 cm)² = 6.25 cm²
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Additional comment
The "square" of a variable is that variable to the second power. The terms 2x or 4x are linear terms with the variable to the first power, do not represent the area of a square.
The equation A(x) = 4x² introduces a multiplier of 4 that is not applicable to the area of a square based on side length. (The formula might be useful if x represents the distance from one side to the center of the square, the radius of an inscribed circle, for example.)
