兩條maths 10分

👨🏻‍🏫 學術台數學

2007-05-07 5:48 am

1

sin20cos310+sin200cos50
=?

====================================

2

sin40+cos140+tan220
--------------------------------- <份線
sin220+cos40+tan140

=?

要有步驟

回答 (2)

用戶40379

2007-05-07 6:09 am

✔ 最佳答案

計法如下

圖片參考：http://hk.geocities.com/namsm4e/p0166.jpg

👍 0 👎 0

2007-05-07 6:27 am

1)
sin20cos310+sin200cos50
=cos(90-20)cos(360-310)-cos(270-200)cos50
=cos70cos50-cos70cos50
=0

2)
sin40+cos140+tan220
---------------------------------
sin220+cos40+tan140

=
cos(90-40)-cos(180-140)+tan(180+40)
---------------------------------------------------------
-cos(270-220)+cos40+tan(180-40)

=
cos50-cos40+tan40
------------------------------
-cos50+cos40-tan40

=
cos50-cos40+tan40
------------------------------
-(cos50-cos40+tan40)

=-1

參考: .

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