2pi is period, 2pi•n where n = 0, ±1, ±2, …. , and that way you find all possible solutions
So, if I wanted to solve sin x = 0, I would take the inverse sine of 0. I get an answer of 0 on my calculator, but in reality, sin x = 0 has an infinite number of solutions. As you can see on the graph, I get 0 for sin x every 2pi spaces. So my answers are actually x = 0 + 2*pi*n where n stands for the number of extra solutions that we have. N increases by 1 each time. We get x = 0 + 2*pi*0 = 0 for our first solution. The next solution is x = 0 + 2*pi*1 = 2pi. The next one is x = 0 + 2*pi*2 = 4pi. And so on and so forth.
The sine and cosine functions both have a period of 2pi. This means that your answers are 2pi spaces apart. The tangent function, on the other hand, has a period of pi. This means that these answers are pi spaces apart.
You can use unit circle too, but you also need to use a period.
