※ 引述《SC333 (SC)》之銘言：
: https://tinyurl.com/yyzdczxz
: 第三大題 填充題的 C.
: 有勞高手解惑 謝謝
不用正弦定理
另解：
theta = t
2 x sin(t/2) = x^2
=> x = 2sin(t/2)
=> sin(t) = 4[sin(t/2)]^2
=> tan(t/2) = 1/2
x^2 = (1/4)x^4 + x^4 => x^2 = 4/5
三角形面積 = (1/2) x^2 sin(t)
= (1/2) (16/25) = 8/25
再解：
theta = t
2 x sin(t/2) = x^2
=> x = 2sin(t/2)
=> sin(t) = 4[sin(t/2)]^2
=> cos(t) = 3/5
=> sin(t) = 4/5 = x^2
三角形面積 = (1/2) x^2 sin(t)
= (1/2) (16/25) = 8/25
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