# Thread: Look here, need help.

1. ## Look here, need help.

I believe I am capable of doing the question. I just have no clue what it is asking me to do. Here's the question:

"Determine the EXACT value of p(7pi/12), that is sin(7pi/12) and cos(7pi/12) by letting alpha = (pi/4) and beta = (pi/3)"

.. Yup, no clue. Help is appreciated.

2. Originally Posted by MathNoobie
I believe I am capable of doing the question. I just have no clue what it is asking me to do. Here's the question:

"Determine the EXACT value of p(7pi/12), that is sin(7pi/12) and cos(7pi/12) by letting alpha = (pi/4) and beta = (pi/3)"

.. Yup, no clue. Help is appreciated.
$\frac{\pi}{4} + \frac{\pi}{3} = \frac{7 \pi }{12}$

So what are $sin(\alpha + \beta)$ and $cos(\alpha + \beta)$?

-Dan

3. Originally Posted by MathNoobie
I believe I am capable of doing the question. I just have no clue what it is asking me to do. Here's the question:

"Determine the EXACT value of p(7pi/12), that is sin(7pi/12) and cos(7pi/12) by letting alpha = (pi/4) and beta = (pi/3)"

.. Yup, no clue. Help is appreciated.
does this help?

$\sin \bigg( \frac {7 \pi}{12} \bigg) = \sin \bigg( \frac {4 \pi}{12} + \frac {3 \pi}{12} \bigg) = \sin \bigg( \frac {\pi}3 + \frac {\pi}4 \bigg) = \sin ( \beta + \alpha )$

a similar manipulation should be done with cosine

Now, you should know that:

$\sin ( \alpha + \beta ) = \sin \alpha \cos \beta + \sin \beta \cos \alpha$

and

$\cos ( \alpha + \beta ) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$