## calyne show me how to calculate -sin(3pi/4) one year ago one year ago

1. Dockworker

you want to get the reference angle, that is the first quadrant angle that has the same value, maybe varying only by sign

2. Dockworker

we know the sign is positive in the 2nd quadrant and in the first quadrant

3. Dockworker

of sine, that is

4. Dockworker

so this question is the exact same thing as -sin(3pi/4-pi/2)

5. Dockworker

which is -sin(pi/4)

6. Dockworker

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?

7. Mertsj

|dw:1333508390565:dw| So $-\sin\frac{3\pi}{4}=-\sin\frac{\pi}{4}=-\frac{\sqrt{2}}{2}$