Hello, sunmalus!

Find the value of

knowing that:

. .

. . . . is in Quadrant 2

The final answer should be: . . I'm not getting this

We have: .

Then:. . . .

Square: .

Then: .

Factor: .

Then: .

And we have: .

What's going on?

Results 1 to 10 of 10

- March 19th 2010, 03:54 PM #1

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## Sin(y)=Cos(y/3)

Hello everyone, I came across an old trigonometry problem which I'm not able to solve again and it's driving me crazy, here it is:

find the value of tan(x+y) knowing that:

tan(x)=-sqrt(2)/2

sin(y)=cos(y/3) with 19pi/4<=y<=5pi ( y in [19pi/4;5pi] ).

The final answer should be tan (x+y)= sqrt(2)-3.

My only problem is that I've a really hard time to find y. I tried to add pi/2 on both side to have cos or sin on both sides but it didn't help then I tried with a variable, pi/3=a => sin(3a)=cos(a) => sin(a)(4cosˆ2(a)-1)=cos(a) but then again it led me to nothing...

Can you please explain to me how to find y.

( I did the problem backwards and you should fin tan(y)=1-sqrt(2)).

Thanks in advance!!

- March 19th 2010, 06:01 PM #2

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- March 19th 2010, 06:28 PM #3

- March 20th 2010, 02:33 AM #4

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- March 20th 2010, 02:51 AM #5

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- March 21st 2010, 04:15 AM #6

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- March 21st 2010, 05:50 AM #7

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- March 21st 2010, 06:39 AM #8

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RJH, I've a last question for you. How did you proceed to find that:

=>

because I looked how you started and I wanted to try to do the rest by myself but I got stuck at that step...

Do you have a methode or something, I know that you want to find something with the same power and I was looking for this, but by just "randomly" trying to find what it could be it would have taken me a while...

So any advice if I come across something like this again?

- March 21st 2010, 07:12 AM #9

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- March 21st 2010, 08:14 AM #10

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