Hey, I have a few questions I just can't seem to get down, looking for some help here...

1)sin2x= 2csc2x-tanx

1-cos2x

2) cos(x+y)cos(x-y)=(cosx)^2 +(cosy)^2 -1

3) (cosx)^6 + (sinx)^6 = 1-3(sinx)^2 + 3(sinx)^4

Thanks in advance! :D

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- May 27th 2010, 02:06 PMorca432Proving Trig Formulas
Hey, I have a few questions I just can't seem to get down, looking for some help here...

1)__sin2x__= 2csc2x-tanx

1-cos2x

2) cos(x+y)cos(x-y)=(cosx)^2 +(cosy)^2 -1

3) (cosx)^6 + (sinx)^6 = 1-3(sinx)^2 + 3(sinx)^4

Thanks in advance! :D - May 27th 2010, 02:35 PMharish21
- May 27th 2010, 02:46 PMharish21
for (3)

since , you can write:

convert all cosines into sines and your proof will be complete. - May 27th 2010, 04:13 PMorca432
- May 27th 2010, 04:54 PMharish21
- May 27th 2010, 04:55 PMpickslides
Here's a little more.

Now expand this.