作者Honor1984 (奈何上天造化弄人？)
看板Math
标题Re: [中学] 一题三角
时间Sun Aug 23 18:18:15 2020
※ 引述《SC333 (SC)》之铭言：
: https://tinyurl.com/yyzdczxz
: 第三大题 填充题的 C.
: 有劳高手解惑 谢谢
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
三角形面积 = (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
三角形面积 = (1/2) x^2 sin(t)
= (1/2) (16/25) = 8/25
--
※ 发信站: 批踢踢实业坊(ptt.cc), 来自: 117.56.175.175 (台湾)
※ 文章网址: https://webptt.com/cn.aspx?n=bbs/Math/M.1598177897.A.606.html