Simplify expression Hi, I need to simplify the following. \(\cos\left(3π+α\right) \) I am unsure of the steps to take to do this. Thanks 
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$\displaystyle \cos(x+y)=\cos{x}\cos{y}\sin{x}\sin{y}$ 
Sorry, I'm still unsure what you mean. Do you mean... \(\cos\left(3π+α\right)= \cos\left(3π\right)\cos\left(α\right)\sin\left(3π\right)\sin\left(α\right) \) ??? I'm behind as and an online student. Teacher and student interaction is at its minimum this semester. Haven't had a reply in my class forum for ages from the teacher. cou 
That's correct. 
Now, do you know what "" and "" are? 
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I've been working with radians as well as degrees, so I assume \(3π\) would be the radian measure or \(540°\) but I don't need values. I'm looking on purplemaths website and I see the identity laws mentioned here. If I do \(\cos(3π)\sin(3π)=1 \) I still have \(\cos(α)\sin(α) \) would the answer be \(\cos(α) \) ? I still don't understand how I can simplify this further. 
$\displaystyle \cos(3\pi + \alpha) = \cos(3\pi)\cos(\alpha)  \sin(3\pi)\sin(\alpha)$ $\displaystyle \cos(3\pi + \alpha) = (1) \cdot \cos(\alpha)  (0) \cdot \sin(\alpha) = \cos(\alpha)$ 
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Dan 
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