trigonometry angles.

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Hello fellow users, I have 2 questions, thanks in advance!

Question 1:
Angle z lies in the second quadrant and http://www.mcgrawhill.ca/school/lear...6/image065.gif . Determine an exact value for sin2z.

K, so when I attempted this question, I got 120/169, I am not sure if it is -120/169, or 120/169.

Question 2:

Given that http://www.mcgrawhill.ca/school/lear...udy_ch4_q6.gif , and y lies in the third quadrant, express http://www.mcgrawhill.ca/school/lear...y_ch4_q6_1.gif as a difference between http://www.mcgrawhill.ca/school/lear...6/image033.gif

and an angle and then apply a confunction identity to find the measure of y.

I legit have no idea what to do for this!

December 3rd 2012, 07:04 PM
Prove It

Re: trigonometry angles.

If angle z is in the second quadrant then $\displaystyle \begin{align*} \cos{z} \end{align*}$ can not possibly have been $\displaystyle \begin{align*} \frac{12}{13} \end{align*}$ ...
December 3rd 2012, 07:11 PM
ahmedb

Re: trigonometry angles.

Quote:

Originally Posted by Prove It

If angle z is in the second quadrant then $\displaystyle \begin{align*} \cos{z} \end{align*}$ can not possibly have been $\displaystyle \begin{align*} \frac{12}{13} \end{align*}$ ...

I meant -12/13
December 3rd 2012, 07:31 PM
Prove It

Re: trigonometry angles.

Well you know that in the second quadrant, $\displaystyle \begin{align*} \sin{(z)} > 0 \end{align*}$ and $\displaystyle \begin{align*} \cos{(z)} < 0 \end{align*}$ , so what do you think $\displaystyle \begin{align*} \sin{(2z)} = 2\sin{(z)}\cos{(z)} \end{align*}$ has to be?
December 3rd 2012, 07:36 PM
ahmedb

Re: trigonometry angles.

Quote:

Originally Posted by Prove It

Well you know that in the second quadrant, $\displaystyle \begin{align*} \sin{(z)} > 0 \end{align*}$ and $\displaystyle \begin{align*} \cos{(z)} < 0 \end{align*}$ , so what do you think $\displaystyle \begin{align*} \sin{(2z)} = 2\sin{(z)}\cos{(z)} \end{align*}$ has to be?

2(5/13)(-12/13)=-120/169? correct?
December 3rd 2012, 07:52 PM
Prove It

Re: trigonometry angles.

Yes, well done :)
December 3rd 2012, 07:56 PM
ahmedb

Re: trigonometry angles.

Quote:

Originally Posted by Prove It

Yes, well done :)

wow, you teach well, and you are very nice! thanks for the help!