## anonymous 5 years ago Find the exact value. Use a sum or difference identity. sin(-105˙)

1. mattfeury

-105 degrees = 255 degrees 255˙ - 180˙= 75˙, so this is a 75 degree angle in the 3rd quadrant of the unit circle, meaning x and y are both negative.

2. anonymous

Omg, thank you so muchh! :D

3. mattfeury

4. anonymous

Thankss!!!

5. anonymous

Wait, but then what is sin(75˙) ?

6. mattfeury

you can use the half angle identity, just like here: http://www.schooltrainer.com/homework-answers/use-a-half-angle-identity-to-find-the-exact-value-sin75-degrees

7. anonymous

That helps but I have to use the Angle Sum/Difference Identities.

8. anonymous

Don't know how Mathematica did it but here is what you will have to shoot for: $\text{Sin}[-105\text{Degree}]=-\frac{1+\sqrt{3}}{2 \sqrt{2}}$