# trigonometry angles.

• Dec 3rd 2012, 06:41 PM
ahmedb
trigonometry angles.
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!
• Dec 3rd 2012, 07:04 PM
Prove It
Re: trigonometry angles.
If angle z is in the second quadrant then \displaystyle \displaystyle \begin{align*} \cos{z} \end{align*} can not possibly have been \displaystyle \displaystyle \begin{align*} \frac{12}{13} \end{align*}...
• Dec 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 \displaystyle \begin{align*} \cos{z} \end{align*} can not possibly have been \displaystyle \displaystyle \begin{align*} \frac{12}{13} \end{align*}...

I meant -12/13
• Dec 3rd 2012, 07:31 PM
Prove It
Re: trigonometry angles.
Well you know that in the second quadrant, \displaystyle \displaystyle \begin{align*} \sin{(z)} > 0 \end{align*} and \displaystyle \displaystyle \begin{align*} \cos{(z)} < 0 \end{align*}, so what do you think \displaystyle \displaystyle \begin{align*} \sin{(2z)} = 2\sin{(z)}\cos{(z)} \end{align*} has to be?
• Dec 3rd 2012, 07:36 PM
ahmedb
Re: trigonometry angles.
Quote:

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

2(5/13)(-12/13)=-120/169? correct?
• Dec 3rd 2012, 07:52 PM
Prove It
Re: trigonometry angles.
Yes, well done :)
• Dec 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!