On this problem, they want you to use your even and odd identities along with the period concept. So the first thing we're going to remember is that sine of negative Theta is really the same thing as negative sine Theta. Couple ways to think about that. If we thought about the unit circle and we thought about this being angle Theta and this being angle negative Theta, we could remember that sine in the first quadrant is positive and sine in the 4th quadrant is negative. We could also think about looking at a regular sine graph. And if we look at our sine graph this way, let's call out here somewhere Theta so that negative Theta is going the opposite direction. We can see that the Y value for Theta versus negative Theta are opposites. So that's one concept we need. We also need to remember the cosine of Theta plus a full circle is really just cosine of Theta and then also we might need tangent of Theta plus Pi is just really tangent of Theta. So those are all going to be important identities that we may use in this problem. So the very first thing, the sine of -39° is going to be negative sine of 39°, cosine of 399 is really going to be cosine of 399 -, 33160. So that's 39 plus tangent 219 -, 180, which is going to be 39. So now we remember that sine over cosine is really just tangent. So negative tangent 39° plus tangent 39° is really just zero.