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The area enclosed by the circle \( r = 2 \) is

  • A.\( 2\pi \)
  • B.\( 8\pi \)
  • C.\( \pi \)
  • D.\( 4\pi \)

Answer: D

Apply the polar formula over a complete revolution:

\[ A \;=\; \frac{1}{2}\int_{0}^{2\pi} 2^{2}\,d\theta \;=\; \frac{1}{2}(4)(2\pi) \;=\; 4\pi. \]

This agrees with \( \pi r^{2} = \pi(4) \). Dropping the half would give \( 8\pi \), and omitting the square would give \( 2\pi \), which is the circumference instead

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