Identities & formulas

2008-11-17 11:14 pm

1) cot X - tan X= (cos 2X)/(sin X cox X)
2) tan (x/2)= tan(sec X +1)
3) cos4x cos5x - sin4x sin5x
4) sin15* cos75* + cos15* sin75*

*=degree

更新1:

For #1 and 2 : Please prove each identity For #3 abd 4: Write eac h expression as a single trigonometric function

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