Author Topic: Double angle formula help (Read 1150 times) Tweet Share

Stick · « **on:** November 11, 2012, 11:37:37 am »

I've never come across this style of question before, so could someone please show me how to do them? Thanks.

- NB: I only need help for part b on Question 12.

pi · « **Reply #1 on:** November 11, 2012, 11:43:55 am »

Hint:

You know cos2a = 1- 2sin^2 a

What if you let a = x/2 ?

Stick · « **Reply #2 on:** November 11, 2012, 11:45:16 am »

Alright, I'll go give that a go now.

EDIT: Alright, I got Question 12, but how about Question 11?

pi · « **Reply #3 on:** November 11, 2012, 12:03:12 pm »

Similar thing, use the tan(2x) formula, but let 2x = pi/4

This one's gonna take a bit more algebra after that though

Stick · « **Reply #4 on:** November 11, 2012, 12:04:02 pm »

Yeah, I thought that was what I had to do - it was what I was trying to do last night, but I got lost in all the algebra.

I'll give it another go now.

pi · « **Reply #5 on:** November 11, 2012, 12:05:08 pm »

Hint: solve the impending quadratic

(N.B if this doesn't make sense, ignore it because I have forgotten too much maths haha)

Stick · « **Reply #6 on:** November 11, 2012, 12:13:01 pm »

Yeah, I just got the answer, but I also got the conjugate of the answer as well. How do I discount the conugate?

WhoTookMyUsername · « **Reply #7 on:** November 11, 2012, 12:14:32 pm »

Look at the quadrant

pi · « **Reply #8 on:** November 11, 2012, 12:14:41 pm »

Quadrant of tan(pi/8)

Stick · « **Reply #9 on:** November 11, 2012, 12:15:41 pm »

Fail. +_+ Thanks guys, as you can see I've probably spent too much time in a Further class.

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