Question

蘋果哈特利

要怎麼確定他是圓內接四邊形
他上面寫的公式是這個四邊形的特別算法嗎？

Answer 1

✨ 最佳解答 ✨

戦場ヶ原ヒタギ✖︎両儀式

Try to think outside of the box!

蘋果哈特利

謝謝

Answer 2

Ny-Ålesund

令 AC = x = x1 + x2、BD = y = y1 + y2
四邊形 ABCD 面積 = △OAB + △OBC + △OCD + △OAD
= 1/2·x1·y1·sinθ + 1/2·x2·y1·sin(π-θ) + 1/2·x2·y1·sin(π-θ) + 1/2·x2·y2·sinθ + 1/2·x1·y2·sin(π-θ)
= 1/2·x1·y1·sinθ + 1/2·x2·y1·sinθ + 1/2·x2·y1·sinθ + 1/2·x2·y2·sinθ + 1/2·x1·y2·sinθ
= 1/2·sinθ·(x1y1 + x2y1 + x2y2 + x1y2)
= 1/2·sinθ·[y1(x1 + x2) + y2(x1 + x2)]
= 1/2·sinθ·(x1 + x2)·(y1 + y2)
= 1/2·x·y·sinθ

蘋果哈特利

你們寫的我都看得懂
所以選先寫的 謝謝！