What does the K in S = {β | β = α + K · 360 °, K ∈ Z} stand for

What does the K in S = {β | β = α + K · 360 °, K ∈ Z} stand for

It's just an unknown number, which can be 1, 2, 3, 4. In this question, it represents the number of circles of a circle, how many 360 degrees are there

Explanation of the angle formula s = {β, β = α = k · 360 °, K ∈ Z}
What do the symbols s, = {β, β, K ∈ Z mean?
I'm not in high school yet. I'm preparing. The textbook doesn't explain these symbols
The formula is wrong, s = {β, β = α + K · 360 °, K ∈ Z}

S stands for a set
β is the element in the set
So β is an integral multiple of 360 degrees
That is to say, all 360 degree integral multiple angles are included in this set
A set is a general term for a class of elements

It is known that the equation about x [K times the square of X + (2k-1) x + 1 + 0] has two real roots x1, x2. (1) find the value range of K (2) whether there is a real root
(2) Is there a real number k, which means that the roots of two real numbers of the equation are opposite to each other? If it exists, find the value of K. if it does not exist, explain the reason.

1. As long as B ^ 2-4ac > 0, k > 1 or K can be obtained