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- 2πa2√232πa2√23\frac{2 \pi a^{2} \sqrt{2}}{3}
- πa2√24\frac{\pi a^{2} \sqrt{2}}{4}
- πa2√2\pi a^{2} \sqrt{2}.
- πa2√22\frac{\pi a^{2} \sqrt{2}}{2}.