Here's the question you clicked on:
calyne
show me how to calculate -sin(3pi/4)
you want to get the reference angle, that is the first quadrant angle that has the same value, maybe varying only by sign
we know the sign is positive in the 2nd quadrant and in the first quadrant
so this question is the exact same thing as -sin(3pi/4-pi/2)
think of the unit circle with radius 1, what would the y-value need to be with respect to the radius for theta to be pi/4?
|dw:1333508390565:dw| So \[-\sin\frac{3\pi}{4}=-\sin\frac{\pi}{4}=-\frac{\sqrt{2}}{2}\]