Sine of 21 Pi force, we need to think about how many full circles is 21 Pi force. Well, four goes into 21 Pi 5 full times with one leftover. But if we want to do it in terms of a unit circle, we know that here's zero and here's π and here's 2π, three Pi, 4 Pi, SO5 Pi is over here with a Pi, fourth more. So we're going to be at sine of five Pi fours cosine PI6 plus cosine 5 Pi force sine PI6. Well, sine of five Pi force is negative root 2 / 2. Cosine of Pi 6 is root 3 / 2. Cosine of π port 5, Pi force is negative root 2 / 2 and sine of Pi 6 is 1/2. So we get negative root 6 minus root 2 all over 4.