點解cos^2 x + sin^2 x =1?
E.G
cos^2 45 + sin^2 45 =1
why?
why : cos^2 x + sin^2 x =1?
2009-05-31 9:06 pm
回答 (6)
2009-05-31 9:19 pm
✔ 最佳答案
這是關係到畢氏定理的請看:
http://img195.imageshack.us/img195/6743/pythtrigoz.png
2009-05-31 14:17:32 補充：
嗯.以上的,誰也知道
2009-05-31 14:18:43 補充：
問得出尼個題目既就未學half-angle啦.
你想佢更加唔明!?
2009-05-31 19:06:30 補充：
用PYTH證咪ok = =
2009-06-02 2:41 am
Let sin x = a / c and cos x = b / c , where c^2 = a^2 + b^2.
Consider
sin^2 x = a^2 / c^2 ; and
cos^2 x = b^2 / c^2 .
Then, we have
sin^2 x + cos^2 x = (a^2 + b^2) / c^2 = c^2 / c^2 = 1.
Therefore, the result follows.
Consider
sin^2 x = a^2 / c^2 ; and
cos^2 x = b^2 / c^2 .
Then, we have
sin^2 x + cos^2 x = (a^2 + b^2) / c^2 = c^2 / c^2 = 1.
Therefore, the result follows.
參考: P8051
2009-06-01 2:09 am
注意邏輯循環！
LHS= cos^2 x + sin^2 x
= 1/2 ( 1 + cos2x ) + 1/2 ( 1- cos2x)
= 1
= RHS
LHS= cos^2 x + sin^2 x
= 1/2 ( 1 + cos2x ) + 1/2 ( 1- cos2x)
= 1
= RHS
2009-05-31 9:34 pm
cos^2 θ+sin^2 θ=1
2009-05-31 9:23 pm
LHS= cos^2 x + sin^2 x
= 1/2 ( 1 + cos2x ) + 1/2 ( 1- cos2x)
= 1
= RHS
所以 cos^2 x + sin^ 2 x congruent to 1
= 1/2 ( 1 + cos2x ) + 1/2 ( 1- cos2x)
= 1
= RHS
所以 cos^2 x + sin^ 2 x congruent to 1
參考: 我既數學知識
2009-05-31 9:10 pm
因為e條係恆等式,,
已經證實左,,
無論代咩答案都係,,1
已經證實左,,
無論代咩答案都係,,1
收錄日期: 2021-04-23 20:44:31
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20090531000051KK00766