1. ## Got 3 questions

i got 3 tough trigonometry questions for you all. Hope you help me solve them out. If necessary i can show you the steps i tried out myself but for
the present i am limiting myself to the questions itself. any help would be highly appreciated and thanks in advance. the questions are with the attachment:

2. Originally Posted by Pulock2009
i got 3 tough trigonometry questions for you all. Hope you help me solve them out. If necessary i can show you the steps i tried out myself but for
the present i am limiting myself to the questions itself. any help would be highly appreciated and thanks in advance. the questions are with the attachment:
Please show the work you have done.

3. 2cos2x - 2cosx + 1 = 0
4(cosx)^2 - 2 - 2cosx + 1 = 0
4(cosx)^2 - 2cosx - 1 = 0

cosx = -b +/- ......... quadratic forumla

Solving it, we get
cosx = (1 + root5)/4 or cosx = (1 - root5)/4
Therefore, x=36 degrees or x=144 degrees

And I suppose in the last one a, b and c add up to 180?

4. ## question

Originally Posted by darknight
2cos2x - 2cosx + 1 = 0
4(cosx)^2 - 2 - 2cosx + 1 = 0
4(cosx)^2 - 2cosx - 1 = 0

cosx = -b +/- ......... quadratic forumla

Solving it, we get
cosx = (1 + root5)/4 or cosx = (1 - root5)/4
Therefore, x=36 degrees or x=144 degrees

And I suppose in the last one a, b and c add up to 180?
i had worked upto the quadratic formulae but after getting the expression how does one knows that it 36 degrees and 144 degrees?also, my work for the second question is in the attachment.

5. Originally Posted by Pulock2009
i had worked upto the quadratic formulae but after getting the expression how does one knows that it 36 degrees and 144 degrees?also, my work for the second question is in the attachment.
The moment I read the reply you got, I've been waiting to see if you asked that. You are probably not expected to know those exact values. Have you asked your instructor if you do?

The derivation of them is not straightforward (but someone will do it if you really really want to know).