## 2002 Winter Diet, paper 2, Q5 cant even get it started

### x_Jo_x

Posted 02 May 2007 - 08:07 PM

i cannot seem to even start this question off and it is really bugging me. I know i have to put in a double angle formula somewhere but i just don't know where or when!

Any help would be great! thank you

### Pete

Posted 02 May 2007 - 08:59 PM

Well, if you look at your formulae list, you'll see that , so:

It is relatively easy to solve from there, but post if you have any problems  Just remember that it's for , so you should end up with four different values.

### Indie_Cindy

Posted 02 May 2007 - 09:06 PM

Hey, im not 100% sure if i did this right, but i got the same answer as thepast paper book.

cos2x - 2sin²x = 0
cos²x - sin²x - 2sin²x = 0
cos²x = sin²x - 2sin²x
cos²x = sinx²(1-2)
cos²x = 1 over 2
cos2x = 1 over 2
cos2x = 60°
cos2x = pie over 6, 5pie over 3
cosx = pie over 6, 5 pie over 6, 7 pie over 6, 11pie over 6

^^^hoped that helped a wee bit

### x_Jo_x

Posted 03 May 2007 - 09:18 PM

hey, thanks guys,, that has really helped. The help was very much appreciated!