A rectangle with one side 4 cm is inscribed in a circle

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A rectangle with one side 4 cm is inscribed in a circle of radius 2.5 cm. The area of the rectangle is :

1. 8 cm²
2. 12 cm²
3. 16 cm²
4. 20 cm²

Correct Option: B

Let AB = 4 cm.
∴ AC = Diameter of circle
= Diagonal of rectangle = 5 cm.
∴ In ∆ABC
BC = √AC² – AB²
= √5² – 4² = √25 – 16
= √9 = 3 cm.
∴ Area of rectangle = 4 × 3 = 12 sq. cm.