Contrary to what religious leaders might lead you to believe, there is nothing wrong with sin. At least not with the mathematical sin. The sinus, sine or sin function tells you the ratio of the lengths of two sides in a right angle triangle.
Let us not talk about triangles, angles and lengths of sides for now, but think of the sin function as a generic function of x: f(x)=sin(x).
f(−x)=−f(x).
f(x)=f(x+2π).
to be confused with (sin(x))−1=1sin(x)≡csc(x).
The function starts from zero sin(0)=0, then goes up to take on the value 1 at x=π4, then falls down until it crosses the x axis at x=π.
After π the function drops below the x axis and reaches its minimum value of −1 at x=3π2 only to come up again and repeat the 2π-long cycle starting from x=2π.
We have 0=sin(0)=sin(π)=sin(2π)=sin(3π)=⋯, in fact sin(x) has a root at each multiples of π.