F.4 A-MATH題唷=.=

2009-02-19 6:03 am

If A + B + C = 180° , prove the following identities.

1. sin2A + sin2B + sin2C = 4sinAsinBsinC

2. sinA + sinB + sin C = 4cosA/2 cosB/2 cosC/2

3. cos2A + cos 2B - cos2C - 1 = -4sinAsinBcosC

4. cos^2A + cos^2B + cos^2C - 1 = -2cosAcosBcosC

有冇人識計唷=.=
如果識就盡量答啦=.=

回答 (1)

用戶7639

2009-02-19 6:44 am

✔ 最佳答案

第2題
As follow AS~~~

圖片參考：http://g.imagehost.org/0403/ScreenHunter_01_Feb_18_22_51.gif

2009-02-18 23:03:03 補充：
1.
http://f.imagehost.org/0467/ScreenHunter_02_Feb_18_23_09.gif

2009-02-18 23:16:42 補充：
3.
http://g.imagehost.org/0916/ScreenHunter_03_Feb_18_23_25.gif

2009-02-18 23:38:55 補充：
4.
http://g.imagehost.org/0588/ScreenHunter_04_Feb_18_23_48.gif

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