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s=â«(αâβ)â(ϲ+Ï'²)dθ
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s=2·s1
=2â«(0âÏ)â[a²(1+cosθ)²+(-asinθ)²]dθ
=2aâ«(0âÏ)â(2+2cosθ)dθ
=4aâ«(0âÏ)cos(θ/2)dθ
=8asin(θ/2) |(0âÏ)
=8a
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