Question 595438
cos(3pi/4) cos(pi)+ sin(3pi/4) sin(pi)


(-sqrt(2)/2)(-1)+ (sqrt(2)/2)(0)


sqrt(2)/2


So <img src="http://latex.codecogs.com/gif.latex?\Large \cos\left(\frac{3\pi}{4}\right)\cos\left(\pi\right)+\sin\left(\frac{3\pi}{4}\right)\sin\left(\pi\right) = \frac{\sqrt{2}}{2}" title="x" />