Do the following rules properly describe at which intervals both the unrestricted sine and cosine functions are negative? Is only one of them right or both?

1) [Xmin - period/4, Xmin + period/4]

2) [x2 + pn, x1 +pn] (p = period) (n = integers)

I'm trying to find similar points using my calculator with these two rules and I can't seem to find any which leads me to believe, I am doing something wrong or these rules are wrong.

Please help!